View source for Medicine:Poliomyelitis eradication

 [[File:Vaccination-polio-india.jpg|thumb|A child receives oral polio vaccine during a 2002 campaign to immunize children in India.]]thumb|[[Poliovirus]]
<!-- Defining the topic and describing the current effort to achieve eradication. -->
'''Poliomyelitis eradication''' refers to a permanent elimination of all cases of [[Medicine:Poliomyelitis|poliomyelitis]] (polio) infection around the world. A public health effort to this end began in 1988, led by the [[Organization:World Health Organization|World Health Organization]] (WHO), the United Nations Children's Fund (UNICEF) and the Rotary Foundation.<ref>{{Cite web|title = Polio Eradication {{!}} Global Health Strategies|url = http://www.globalhealthstrategies.com/issues/polio-eradication|website = www.globalhealthstrategies.com|access-date = 11 February 2016|first = Global Health|last = Strategies}}</ref>  These organizations, along with the U.S. Centers for Disease Control and Prevention (CDC) and The Gates Foundation, have spearheaded the campaign through the [[Organization:Global Polio Eradication Initiative|Global Polio Eradication Initiative]] (GPEI), which helps to coordinate vaccination campaigns, environmental monitoring, evaluation of possible polio cases and logistics.{{citation needed|date=July 2018}} Successful [[Biology:Eradication of infectious diseases|eradication]] of infectious diseases has been achieved twice before, with [[Medicine:Smallpox|smallpox]]<ref name="WHO_smallpox">{{cite web |title=Smallpox [Fact Sheet] |publisher=[[Organization:World Health Organization|World Health Organization]] |url=http://www.who.int/mediacentre/factsheets/smallpox/en/ |archiveurl=https://web.archive.org/web/20110203051426/http://www.who.int/mediacentre/factsheets/smallpox/en/ |archivedate=3 February 2011 |accessdate=9 November 2013}}</ref> and [[Biology:Rinderpest|rinderpest]].<ref name="bbc">{{cite news |title=UN 'confident' disease has been wiped out |url=https://www.bbc.co.uk/news/science-environment-11542653 |publisher=BBC News |date=14 October 2010 |accessdate=14 October 2010}}</ref>

<!-- The means by which eradication is attempted (i.e. vaccination). -->
Prevention of disease spread is accomplished by vaccination. There are two kinds of [[Engineering:Polio vaccine|polio vaccine]]—oral polio vaccine (OPV), which uses [[Medicine:Attenuated vaccine|weakened poliovirus]], and [[Medicine:Inactivated vaccine|inactivated]] polio vaccine (IPV), which is injected.  The OPV is less expensive and easier to administer, and can spread immunity beyond the person vaccinated, creating [[Medicine:Contact immunity|contact immunity]]. It has been the predominant vaccine used. However, under conditions of long-term vaccine virus circulation in under-vaccinated populations, mutations can reactivate the virus to produce a polio-inducing strain, while the OPV can also, in rare circumstances, induce polio or persistent asymptomatic infection in vaccinated individuals, particularly those that are immunodeficient. Being inactivated, the IPV is free of these risks but does not induce contact immunity. IPV is more costly and the logistics of delivery are more challenging.

<!-- Progress thus far. --> 
The 22 diagnosed wild polio virus (WPV) cases worldwide in 2017{{Update after|2019|02}} represented a {{Percentage|{{#expr:719-22}}|719}} reduction from the 719 diagnosed cases in 2000 and a {{Percentage|{{#expr:350000-22}}|350000|2}} reduction from the estimated 350,000 cases when the eradication effort began in 1988. Of the three strains of polio virus, the last recorded wild case caused by type 2 (WPV2) was in 1999, and WPV2 was declared eradicated in 2015. Type 3 (WPV3) is last known to have caused polio on 11 November 2012, with all wild-virus cases since that date being due to type 1 (WPV1).  All three types are represented among the periodic cases arising from mutated oral vaccine strains, so-called circulating vaccine-derived poliovirus (cVDPV). {{wipe|India}} is the latest country to have officially stopped endemic transmission of polio, with its last reported case in 2011.<ref>{{cite news |author=Mahr, Krista |title=How India Fought Polio&nbsp;—and Won |url=http://world.time.com/2013/01/13/how-india-fought-polio-and-won/ |work={{wipe|Time (magazine)}} |date=13 January 2013 |accessdate=28 February 2013}}</ref> Three countries remain where the disease is endemic—Afghanistan, Pakistan and Nigeria.

== Factors influencing eradication of polio ==

Eradication of polio has been defined in various ways—as elimination of the occurrence of poliomyelitis even in the absence of human intervention,<ref name=Barrett>{{cite journal|title=Eradication versus control: the economics of global infectious disease policies |journal=Bull World Health Organ |year=2004| author = Barrett S |volume=82|issue=9|pages=683–8|pmid = 15628206 |url=|pmc=2622975}}</ref> as [[Biology:Extinction|extinction]] of [[Biology:Poliovirus|poliovirus]], such that the infectious agent no longer exists in nature or in the laboratory,<ref>{{cite journal |author=Cockburn T |title=Eradication of infectious diseases |journal=Science |volume=133 |issue= 3458|pages=1050–8 |year= 1961|pmid=13694225 |doi=10.1126/science.133.3458.1050 |bibcode=1961Sci...133.1050C}}</ref> as control of an infection to the point at which [[Medicine:Transmission|transmission]] of the disease ceased within a specified area,<ref name=Barrett /> and as reduction of the worldwide incidence of poliomyelitis to zero as a result of deliberate efforts, and requiring no further control measures.<ref>{{cite journal|title=Recommendations of the International Task Force for Disease Eradication |journal=Morbidity and Mortality Weekly Report|year=1993|author=[No authors listed] | volume=42 |pages=(RR–16):1–38 |pmid = 8145708 |url=https://www.cdc.gov/mmwr/preview/mmwrhtml/00025967.htm |accessdate=13 April 2007|issue=RR-16}}</ref>

In theory, if the right tools were available, it would be possible to eradicate all infectious diseases that reside only in a human host. In reality there are distinct biological features of the organisms and technical factors of dealing with them that make their potential eradicability more or less likely. Three indicators, however, are considered of primary importance in determining the likelihood of successful eradication: that effective interventional tools are available to interrupt transmission of the agent, such as a [[Biology:Vaccine|vaccine]]; that diagnostic tools, with sufficient sensitivity and specificity, be available to detect infections that can lead to transmission of the disease; and that humans are required for the life-cycle of the agent, which has no other [[Biology:Vertebrate|vertebrate]] [[Biology:Natural reservoir|reservoir]] and cannot amplify in the environment.<ref>General: Centers for Disease Control and Prevention. Global disease elimination and eradication as public health strategies. MMWR 1999;48(Suppl). Specific: Centers for Disease Control and Prevention. [https://www.cdc.gov/mmwr/preview/mmwrhtml/su48a7.htm The Principles of Disease Elimination and Eradication.] In: Global disease elimination and eradication as public health strategies. MMWR 1999;48(Suppl).</ref>

=== Strategy ===
The most important step in eradication of polio is interruption of endemic [[Medicine:Transmission|transmission]] of poliovirus. Stopping polio transmission has been pursued through a combination of routine [[Biology:Immunization|immunization]], supplementary immunization campaigns and surveillance of possible outbreaks. Several key strategies have been outlined for stopping polio transmission:<ref>{{cite book | author = World Health Organization | title = Global polio eradication initiative: strategic plan 2004–2008 | publisher = WHO | year = 2003 | location = Geneva | url = http://www.polioeradication.org/content/publications/2004stratplan.pdf | isbn = 92-4-159117-X | format = PDF | deadurl = yes | archiveurl = https://web.archive.org/web/20070927204236/http://www.polioeradication.org/content/publications/2004stratplan.pdf | archivedate = 27 September 2007 | df = dmy-all }}</ref>

# High infant immunization coverage with four doses of oral [[Engineering:Polio vaccine|polio vaccine]] (OPV) in the first year of life in developing and endemic countries, and routine immunization with OPV and/or IPV elsewhere.
# Organization of "national immunization days" to provide supplementary doses of oral polio vaccine to all children less than five years old.
# Active surveillance for poliovirus through reporting and laboratory testing of all cases of acute flaccid paralysis. Acute flaccid paralysis (AFP) is a clinical manifestation of poliomyelitis characterized by weakness or [[Engineering:Paralysis|paralysis]] and reduced [[Biology:Muscle tone|muscle tone]] without other obvious cause (e.g., trauma) among children less than fifteen years old. AFP is also associated with a number of other pathogenic agents including [[Biology:Enterovirus|enterovirus]]es, [[Biology:Echovirus|echovirus]]es, and adenoviruses, among others.<ref>{{cite web | title = Acute Flaccid Paralysis | work = Public Health Notifiable Disease Management Guidelines | publisher = Alberta Government Health and Wellness | year = 2005 | url = http://www.health.alberta.ca/documents/Guidelines-Acute-Flaccid-Paralysis-AFP-2011.pdf | accessdate = 31 July 2007|format=PDF}}</ref>
# Expanded environmental surveillance to detect the presence of poliovirus in communities.<ref name="surveillance">{{cite report|title=Polio Environmental Surveillance Expansion Plan : Global Expansion Plan under the Endgame Strategy 2013-2018|publisher=GPEI|date=April 2015|access-date=1 July 2018 | url=http://polioeradication.org/wp-content/uploads/2016/07/GPLN_ExpansionPlanES.pdf}}</ref>  Sewage samples are collected at regular and random sites and tested in laboratories for the presence of WPV or cVDPV.   Since most polio infections are asymptomatic, transmission can occur in spite of the absence of polio-related AFP cases, and such monitoring helps to evaluate the degree to which virus continues to circulate in an area.
# Targeted "mop-up" campaigns once poliovirus transmission is limited to a specific focal area.

=== Vaccination ===
There are two distinct [[Engineering:Polio vaccine|polio vaccine]]s.  The oral polio vaccine (OPV, or Sabin vaccine) contains an [[Medicine:Attenuated vaccine|attenuated]] poliovirus, 10,000 times less able to enter the circulation and cause polio,<ref name="GPEI-OPV">{{cite web| url=http://polioeradication.org/polio-today/polio-prevention/the-vaccines/opv/ | title=OPV | publisher=GPEI | access-date=7 July 2018}}</ref> delivered as oral drops or infused into sugar cubes.  It is highly effective and inexpensive (about {{wipe|United States dollar}}0.12 per dose in 2016<ref name="GPEI-OPV" />) and its availability has bolstered efforts to eradicate polio. A study carried out in an isolated Eskimo village showed that [[Biology:Antibody|antibodies]] produced from subclinical wild virus infection persisted for at least 40 years.<ref name=Paul_1951>{{cite journal |vauthors=Paul J, Riordan J, Melnick J |title=Antibodies to three different antigenic types of poliomyelitis virus in sera from North Alaskan Eskimos |journal=Am J Hyg |volume=54 |issue=2 |pages=275–85 |year=1951 |pmid=14877808 }}</ref> Because the [[Biology:Immune response|immune response]] to oral polio vaccine is very similar to natural polio infection, it is expected that oral polio vaccination provides similar lifelong [[Medicine:Immunity (medical)|immunity]] to the virus.<ref name="Watch">{{cite web|url=http://www.worldwatch.org/node/1644|title=Eradicating Polio: A Model for International Cooperation|last=Mastny|first=Lisa|date=25 January 1999|website=|publisher=Worldwatch Institute|archive-url=https://web.archive.org/web/20060608165205/http://www.worldwatch.org/node/1644|archive-date=2006-06-08|dead-url=|accessdate=2 February 2007}}</ref><ref name=Robertson_1993>Robertson, Susan. (1993) The Immunological Basis for Immunization Series. [http://www.who.int/ihr/polio1993en.pdf Module 6: Poliomyelitis.] World Health Organization. Geneva, Switzerland.</ref>  Due to its route of administration, it induces an immunization of the intestinal mucosa that protects against subsequent infection, though multiple doses are necessary to achieve effective prophylaxis.<ref name="GPEI-OPV" />  It can also produce [[Medicine:Contact immunity|contact immunity]].  [[Medicine:Attenuated vaccine|Attenuated]] poliovirus derived from the oral polio vaccine is excreted, and infects and indirectly induces immunity in unvaccinated individuals, thus amplifying the effects of the doses delivered.<ref name= Nathan>{{cite journal |vauthors=Nathanson N, Martin J |title=The epidemiology of poliomyelitis: enigmas surrounding its appearance, epidemicity, and disappearance |journal=Am J Epidemiol |volume=110 |issue=6 |pages=672–92 |year=1979 |pmid=400274 |doi=10.1093/oxfordjournals.aje.a112848}}</ref>  The oral administration does not require special medical equipment or training.  Taken together, these advantages have made it the preferred vaccine of many countries, and it has long been preferred by the global eradication initiative.<ref name="GPEI-OPV" />

The primary disadvantage of the OPV derives from its inherent nature as an attenuated but active virus.  It can induce vaccine-associated paralytic poliomyelitis (VAPP) in approximately 1 individual per every 2.4 million doses administered.<ref name="WHO-polio vaccine">{{cite web| url=http://www.who.int/ith/vaccines/polio/en/ | title=International travel and health: Poliomyelitis (Polio) | publisher=WHO | access-date=7 July 2018}}</ref>  Likewise, mutation during the course of persistent circulation in undervaccinated populations can lead to vaccine-derived poliovirus strains (cVDPV) that can induce polio at much higher rates.<ref name="WHO-polio vaccine" />  Until recently, a trivalent OPV containing all three virus strains was used, but with the eradication of wild poliovirus type 2 this was phased out in 2016 and replaced with bivalent vaccine containing just types 1 and 3, while use of monovalent type 2 OPV is restricted to regions with documented cVDPV2 circulation.<ref name="GPEI-OPV" />

The inactivated polio vaccine (IPV, or Salk) contains trivalent fully inactivated virus, administered by injection.  This vaccine cannot induce VAPP nor do cVDPV strains arise from it, but it likewise cannot induce contact immunity and thus must be administered to every individual.  Added to this are greater logistical challenges. Though a single dose is sufficient for protection, administration requires medically trained vaccinators armed with single-use needles and syringes.  Taken together, these factors result in substantially higher delivery costs.<ref name="GPEI-IPV">{{cite web| url=http://polioeradication.org/polio-today/polio-prevention/the-vaccines/ipv/ | title=IPV | publisher=GPEI | access-date=7 July 2018}}</ref>  Original protocols involved [[Biology:Intramuscular injection|intramuscular injection]] in the arm or leg, but recently [[Medicine:Subcutaneous injection|subcutaneous injection]] using a lower dose (so-called fractional-dose IPV, fIPV) has been found to be effective, lowering costs and also allowing for more convenient and cost-effective delivery systems.<ref name="Bahl">{{cite journal|vauthors=Bahl S, Verma H, Bhatnagar P, Haldar P, Satapathy A, Kumar K, Horton J, Estivariz C, Anand A, Sutter R|url=https://www.cdc.gov/mmwr/volumes/65/wr/mm6533a5.htm|title=Fractional-Dose Inactivated Poliovirus Vaccine Immunization Campaign — Telangana State, India, June 2016|journal=Morbidity and Mortality Weekly Report|date=2016|volume=65|pages=859–863|doi=10.15585/mmwr.mm6533a5}}</ref><ref>{{cite journal|authors=Hiromasa Okayasu, Carolyn Sein, Diana Chang Blanc, Alejandro Ramirez Gonzalez, Darin Zehrung, Courtney Jarrahian, Grace Macklin, Roland W. Sutter | title=Intradermal Administration of Fractional Doses of Inactivated Poliovirus Vaccine: A Dose-Sparing Option for Polio Immunization | journal=The Journal of Infectious Diseases | year=2017 | volume=216 | number=S1 | pages=S161–7 | url=http://www.who.int/immunization/sage/meetings/2017/october/7_polio_Okayasu_JID2017.pdf | doi=10.1093/infdis/jix038}}</ref>   The use of IPV results in serum immunity, but no intestinal immunity arises.  As a consequence, a vaccinated individual is protected from contracting polio, but their intestinal mucosa can still be infected and serve as a reservoir for the excretion of live virus.  For this reason, IPV is ineffective at halting ongoing outbreaks of WPV or cVDPV, but it has become the vaccine for choice for industrialized, polio-free countries.<ref name="GPEI-IPV" />

While IPV does not itself induce mucosal immunity, it has been shown to boost the mucosal immunity from OPV,<ref>{{cite journal|authors=Edward P K Parker, Natalie A Molodecky, Margarita Pons-Salort, Kathleen M O’Reilly, Nicholas C Grassly | title=Impact of inactivated poliovirus vaccine on mucosal immunity: implications for the polio eradication endgame | journal=Expert Review of Vaccines | year=2015 | volume=14 | number=8 | pages=1113–1123 | doi=10.1586/14760584.2015.1052800}}</ref> and WHO now favors a combined protocol. It is recommended that vulnerable children receive a dose of OPV at birth, then beginning at the age of 6 weeks a 'primary series' consisting of three OPV doses at least four weeks apart, along with one dose of IPV after 14 weeks.<ref name="WHO-polio vaccine" />  This combined IPV/OPV approach has also been used in outbreak suppression.<ref>{{cite news | last=Branswell | first=Helen | title=Combination of oral, injectable polio vaccine used for first time in outbreak | date=20 March 2014 | access-date=7 July 2018 | publisher=CTV | url=https://www.ctvnews.ca/health/combination-of-oral-injectable-polio-vaccine-used-for-first-time-in-outbreak-1.1738666}}</ref>

==== Herd immunity ====
Polio vaccination is also important in the development of ''[[Medicine:Herd immunity|herd immunity]]''.<ref name= Fine>{{cite journal |author=Fine P |title=Herd immunity: history, theory, practice |journal=Epidemiol Rev |volume=15 |issue=2 |pages=265–302 |year=1993 |pmid=8174658}}</ref> For polio to occur in a population, there needs to be an infecting organism ([[Biology:Poliovirus|poliovirus]]), a susceptible human population, and a cycle of [[Medicine:Transmission|transmission]]. Poliovirus is transmitted only through person-to-person contact and the transmission cycle of polio is from one infected person to another person susceptible to the disease, and so on.<ref name= Nathan/> If the vast majority of the population is immune to a particular agent, the ability of that [[Biology:Pathogen|pathogen]] to infect another host is reduced; the cycle of transmission is interrupted, and the pathogen cannot reproduce and dies out. This concept, called community immunity or herd immunity, is important to disease eradication, because it means that it is not necessary to inoculate 100% of the population—a goal that is often logistically very difficult—to achieve the desired result. If the number of susceptible individuals can be reduced to a sufficiently small number through [[Biology:Vaccination|vaccination]], then the pathogen will eventually die off.<ref>{{Cite journal|last=Shaw|first=L.|last2=Spears|first2=W.|last3=Billings|first3=L.|last4=Maxim|first4=P.|date=2010-10-01|year=|title=Effective Vaccination Policies|journal=Information sciences|volume=180|issue=19|pages=3728–3744|doi=10.1016/j.ins.2010.06.005|issn=0020-0255|pmc=2967767|pmid=21057602|via=}}</ref>

When many hosts are vaccinated, especially simultaneously, the transmission of wild virus is blocked, and the virus is unable to find another susceptible individual to infect. Because poliovirus can only survive for a short time in the environment (a few weeks at room temperature, and a few months at 0–8&nbsp;°C (32–46&nbsp;°F)), without a human host the virus dies out.<ref name=Minor_1990>{{cite book |vauthors=Minor PD, Bel EJ | title = Picornaviridae (excluding Rhinovirus). In: Topley & Wilson's Principles of Bacteriology, Virology and Immunity (volume 4) | edition = 8th | pages = 324–357 | publisher = London: Edward Arnold | year = 1990 | isbn = 0-7131-4592-7 }}</ref>

Herd immunity is an important supplement to vaccination. Among those individuals who receive oral polio vaccine, only 95 percent will develop immunity.<ref name = PinkBook>{{cite book | author = Atkinson W, Hamborsky J, McIntyre L, Wolfe S, eds. | title = Epidemiology and Prevention of Vaccine-Preventable Diseases (The Pink Book) | edition = 10th | location = Washington, D.C. | publisher = Public Health Foundation | year = 2007 | url = https://www.cdc.gov/vaccines/pubs/pinkbook/downloads/polio.pdf | id = ISBN |format=PDF}}</ref> That means five of every 100 given the vaccine will not develop any immunity and will be susceptible to developing polio. According to the concepts of herd immunity this population whom the vaccine fails, are still protected by the immunity of those around them. Herd immunity can only be achieved when vaccination levels are high.<ref name= Fine/> It is estimated that 80–86 percent of individuals in a population must be immune to polio for the susceptible individuals to be protected by herd immunity.<ref name= Fine/> If routine immunization were stopped, the number of unvaccinated, susceptible individuals would soon exceed the capability of herd immunity to protect them.<ref>{{cite journal |vauthors=Duintjer Tebbens R, Pallansch M, Kew O, Cáceres V, Sutter R, Thompson K |title=A dynamic model of poliomyelitis outbreaks: learning from the past to help inform the future |url= http://aje.oxfordjournals.org/cgi/content/full/162/4/358 |journal=Am J Epidemiol |volume=162 |issue=4 |pages=358–72 |year=2005 |pmid=16014773 |doi=10.1093/aje/kwi206}}</ref>

==== Vaccine-derived poliovirus ====
[[File:Number of cVDPV cases since 2000.png|thumb|Number of cVDPV cases over time]]
While vaccination has played an instrumental role in the reduction of polio cases worldwide, the use of attenuated virus in the oral vaccine carries with it an inherent risk.  The oral vaccine is a powerful tool in fighting polio in part because of its person-to-person transmission and resulting contact immunity.  However, under conditions of long-term circulation in under-vaccinated populations, the virus can accumulate mutations that reverse the attenuation and result in vaccine virus strains that themselves cause polio.  As a result of such circulating vaccine-derived poliovirus (cVDPV) strains, polio outbreaks have periodically recurred in regions that have long been free of the wild virus, but where vaccination rates have fallen.  Oral vaccines can also give rise to persistent infection in immunodeficient individuals, with the virus eventually mutating into a more virulent immunodeficiency-associated vaccine-derived poliovirus (iVDPV).  In particular the type 2 strain seems prone to reversions, so in 2016 the eradication effort abandoned the trivalent oral vaccine containing attenuated strains of all three virus types, and replaced it with a bivalent oral vaccine lacking the type 2 virus.  Eradication efforts will eventually require all oral vaccination to be discontinued in favor of the use of injectable vaccines.  These vaccines are more expensive and harder to deliver, and they lack the ability to induce contact immunity because they contain only killed virus, but they likewise are incapable of giving rise to vaccine-derived viral strains.<ref>{{cite web|title=Vaccine-Derived Poliovirus|publisher=GPEI|access-date=26 June 2018|url=http://polioeradication.org/polio-today/polio-prevention/the-virus/vaccine-derived-polio-viruses/}}</ref><ref>{{cite journal|last1=Duintjer Tebbens | first1=Radboud J. | last2=Thompson |first2=Kimberly M. |title=Managing the risk of circulating vaccine-derived poliovirus during the endgame: oral poliovirus vaccine needs|journal=BMC Infectious Diseases|volume=15|page=390|year=2015|doi=10.1186/s12879-015-1114-6}}</ref>

=== Obstacles ===

Among the greatest obstacles to global polio eradication are the lack of basic health infrastructure, which limits vaccine distribution and delivery, the crippling effects of civil war and internal strife, and the sometimes oppositional stance that marginalized communities take against what is perceived as a potentially hostile intervention by outsiders. Another challenge has been maintaining the [[Chemistry:Potency (pharmacology)|potency]] of live (attenuated) vaccines in extremely hot or remote areas. The oral polio vaccine must be kept at {{convert|2|to|8|C|F}} for vaccination to be successful.<ref name= Watch/>

An independent evaluation of obstacles to polio eradication requested by the WHO and conducted in 2009 considered the major obstacles in detail by country. In Afghanistan and Pakistan, they concluded that the most significant barrier was insecurity; but that managing human resources, political pressures, the movement of large populations between and within both countries, inadequately resourced health facilities, also posed problems, as well as technical issues with the vaccine. In {{wipe|India}}, the major challenge appeared to be the high efficiency of transmission within the populations of Bihar and Uttar Pradesh states, set against the low (~80% after three doses against type 1) [[Biology:Seroconversion|seroconversion]] response seen from the vaccine. In Nigeria, meanwhile, the most critical barriers identified were management issues, in particular the highly variable importance ascribed to polio by different authorities at the local government level, although funding issues, community perceptions of vaccine safety, inadequate mobilisation of community groups, and issues with the cold chain also played a role. Finally, in those countries where international spread from endemic countries had resulted in transmission becoming re-established—namely Angola, Chad, and South Sudan, the key issues identified were underdeveloped health systems and low routine vaccine coverage, although low resources committed to Angola and South Sudan for the purpose of curtailing the spread of polio and climatic factors were also identified as playing a role.<ref name=evaluation>{{cite web|title=Polio Eradication Evaluation |url=http://www.polioeradication.org/content/general/Polio_Evaluation_Report.asp |accessdate=19 February 2008 |deadurl=yes |archiveurl=https://web.archive.org/web/20100706172238/http://www.polioeradication.org/content/general/Polio_Evaluation_Report.asp |archivedate=6 July 2010 }}</ref>

Two additional challenges are found in unobserved polio transmission and in vaccine-derived poliovirus. First, most polio infections are asymptomatic or result in minor symptoms, with less than 1% of infections leading to paralysis<ref>{{cite web |title=Poliomyelitis |publisher= WHO |url=http://www.who.int/biologicals/areas/vaccines/poliomyelitis/en/}}</ref> and most infected people are unaware that they carry the disease, allowing polio to spread widely before cases are seen.<ref>{{Cite web|title = Polio and Prevention |url=http://www.polioeradication.org/Polioandprevention.aspx |website=www.polioeradication.org |accessdate =13 September 2015}}</ref> In 2000 using new screening techniques for the molecular characterization of outbreak viral strains, it was discovered that some of the outbreaks taking place were actually caused by circulating vaccine-derived poliovirus, following mutations or recombinations in the attenuated strain used for the oral polio vaccine.  This altered the strategy envisioned for the discontinuation of vaccination following polio eradication,<ref>{{Cite journal |title=Ending Use of Oral Poliovirus Vaccine — A Difficult Move in the Polio Endgame| author=Mark A. Pallansch |journal=NEJM |volume=379 |pages=801–803 |doi=10.1056/NEJMp1808903 |year=2018}}</ref> necessitating an eventual switch to the more expensive and logistically more problematic inactivated polio vaccine, since continued use of the oral inactivated virus would continue to produce such revertant infection-causing strains.<ref name=bumpyroad>{{Cite journal |title=The Bumpy Road to Polio Eradication| author=John F Maudlin |journal=NEJM |volume=362 |pages=2346–2349 |doi=10.1056/nejmp1005405 |url=http://content.nejm.org/cgi/content/full/362/25/2346 |year=2010}}</ref> The risk of vaccine-derived polio will persist long after the switch to inactivated vaccine, since a small number of [[Medicine:Asymptomatic carrier|chronic excretor]]s continue to produce active virus for years (or even decades) after their initial exposure to the oral vaccine.<ref>{{Cite journal| title=Update on Vaccine-Derived Polioviruses — Worldwide, January 2014–March 2015|author1=Ousmane M. Diop |author2=Cara C. Burns |author3=Roland W. Sutter |author4=Steven G. Wassilak |author5=Olen M. Kew | journal=Morbidity and Mortality Weekly Report |volume=64 | pages=640–646| url=https://www.cdc.gov/mmwr/preview/mmwrhtml/mm6423a4.htm}}</ref>

In a 2012 interview with Pakistani newspaper ''Dawn'', Dr. Hussain A. Gezari, WHO's special envoy on global polio eradication and primary healthcare, gave his views on obstacles to eradication. He said the biggest hurdle in making Pakistan polio-free was holding district health officials properly accountable—in national eradication campaigns officials had hired their own relatives, even young children. "How do you expect a seven-year-old thumb-sucking kid to implement a polio campaign of the government," said Dr Gezari. He added that, in spite of this, "the first national campaign was initiated by your government in 1994 and that year Pakistan reported 25,000 polio cases, and the number was just 198 last year, which clearly shows that the programme is working."<ref name="WHO rejects rumours"/>

====Opposition to vaccination efforts====

One factor contributing to the continued circulation of polio immunization programs has been opposition in some countries.<ref name="Religious opposition"/>

In the context of the United States invasion of Afghanistan and the subsequent 2003 invasion of Iraq, rumours arose in the Muslim world that immunization campaigns were using intentionally-contaminated vaccines to sterilize local Muslim populations or to infect them with [[Biology:HIV|HIV]].  In Nigeria these rumours fit in with a longstanding suspicion of modern biomedicine, which since its introduction during the era of [[Social:Colonialism|colonialism]] has been viewed as a projection of the power of western nations.   Refusal of vaccination came to be viewed as resistance to western expansionism, and when the contamination rumours led the Nigerian Supreme Council for Sharia to call for a region-wide boycott of polio vaccination, polio cases in the country increased more than five-fold between 2002 and 2006, with the uncontrolled virus then spreading across Africa and globally.<ref name=Ghani>{{cite journal |last1=Ghani |first1=Isaac |last2=Willott |first2=Chris |last3=Dadari |first3=Ibrahim |last4=Larson |first4=Heidi J. |title=Listening to the rumours: What the northern Nigeria polio vaccine boycott can tell us ten years on |journal=Global Public Health |volume=8 |pages=1138-1150 |year=2013 |doi=10.1080/17441692.2013.859720}}</ref><ref name=Njeru >{{cite journal|title=Did the call for boycott by the Catholic bishops affect the polio vaccination coverage in Kenya in 2015? A cross-sectional study |last1=Njeru |first1=Ian |last2=Ajack |first2=Yusuf |last3=Muitherero |first3=Charles |last4=Onyango |first4=Dickens |last5=Musyoka |first5=Johnny |last6=Onuekusi |first6=Iheoma |last7=Kioko |first7=Jackson |last8=Muraguri |first8=Nicholas |last9=David |first9=Robert |journal=Pan African Medical Journal|volume=24|page=120|year=2016|doi= 10.11604/pamj.2016.24.120.8986}}</ref>  In Afghanistan and Pakistan, fears that the vaccine contained contraceptives were one reason given by the [[Religion:Taliban|Taliban]] in issuing ''[[Religion:Fatwa|fatwa]]s'' against polio vaccination.<ref>{{cite web|url=http://wwwnc.cdc.gov/eid/article/15/6/09-0087_article.htm |title=Religious Opposition to Polio Vaccination - Volume 15, Number 6—June 2009—Emerging Infectious Disease journal—CDC |publisher=C.cdc.gov |date=8 December 2010 |accessdate=29 March 2014}}</ref><ref>{{cite web|author=Declan Walsh in Peshawar |url=https://www.theguardian.com/world/2007/feb/15/pakistan.topstories3 |title=Polio cases jump in Pakistan as clerics declare vaccination an American plot &#124; World news |publisher=The Guardian |date=15 February 2007 |accessdate=29 March 2014}}</ref><ref name=Njeru />  Skepticism in the Muslim world was exacerbated when it was learned in 2011 that the Central Intelligence Agency (CIA) had conducted a fake [[Medicine:Hepatitis B|hepatitis B]] immunization campaign to collect blood samples from Osama bin Laden's Abbottabad compound in order to confirm the genetic identity of the children living there, and by implication his own presence, leading directly to his killing.<ref name="Heidi Larson">{{cite news|title=The CIA's fake vaccination drive has damaged the battle against polio|url=https://www.theguardian.com/commentisfree/2012/may/27/cia-fake-vaccination-polio|accessdate=3 June 2012|newspaper=The Guardian|date=27 May 2012|author=Heidi Larson}}</ref><ref name="BBC20111006">{{cite web|url=https://www.bbc.co.uk/news/world-south-asia-15206639|title=Bin Laden death: 'CIA doctor' accused of treason|publisher=BBC News|date=6 October 2011|accessdate=8 October 2011}}</ref> In a letter written to CIA director Leon Panetta, the InterAction Alliance, a union of about 200 U.S.-based non-government organizations, deplored the actions of the CIA in using a vaccination campaign as a cover.<ref name="Dawn: NGO assail CIA">{{cite news|author=Imran Ali Teepu|title=American NGOs assail CIA over fake polio drive|url=http://dawn.com/2012/03/02/american-ngos-assail-cia-over-fake-polio-drive/|accessdate=27 May 2012|newspaper=Dawn|date=2 March 2012}}</ref> Pakistan reported the world's highest number of polio cases (198)<ref name="WHO rejects rumours"/><ref name="Orla Guerin">{{cite news|title='Emergency plan' to eradicate polio launched|url=https://www.bbc.co.uk/news/health-18186393|accessdate=27 May 2012|newspaper=BBC News|date=24 May 2012|author=Orla Guerin}}</ref> in 2011.<ref name="Saeed Shah">{{cite news|title=CIA tactics to trap Bin Laden linked with polio crisis, say aid groups|url=https://www.theguardian.com/world/2012/mar/02/aid-groups-cia-osama-bin-laden-polio-crisis/print|accessdate=27 May 2012|newspaper=The Guardian|date=2 March 2012|author=Saeed Shah}}</ref>  Religious boycotts based on contamination concerns have not been limited to the Muslim world.  In 2015, after claiming that a tetanus vaccine contained a contraceptive, a group of Kenyan Catholic bishops called on their followers to boycott a planned round of polio vaccination.  This did not have a major effect on vaccination rates, and dialog along with vaccine testing forestalled further boycott calls.<ref name=Njeru />

Other religion-inspired refusals arise from concerns over whether the virus contains pig-derived products, and hence are ''haran'' (forbidden) in Islam,<ref>{{cite journal|title=Outbreak of vaccine-preventable diseases in Muslim majority countries|last1=Ahmed|first1=Ali|last2=Lee|first2=Kah S.|last3=Bukhsh|first3=Allah|last4=Al-Worafi|first4=Yaser M.|last5=Sarker|first5=Moklesur|last6=Ming|first6=Long C.|last7=Khan|first7=Tahir M.|journal=Journal of Infection and Public Health|volume=11|issue=2|year=2018|pages=153-155|doi=10.1016/j.jiph.2017.09.007}}</ref> prohibitions against taking of animal life that may be required for vaccine production,<ref name=Njeru /> or a resistance to interfering with divinely-directed disease processes.<ref name=Ghani /><ref name=Njeru />  Concerns were addressed through extensive outreach, directed both toward the communities involved and respected clerical bodies, as well as promoting local ownership of the eradication campaign in each region.  In early 2012, some parents refused to get their children vaccinated in Khyber Pakhtunkhwa and in the Federally Administered Tribal Areas (FATA) but religious refusals in the rest of the country had "decreased manifold".<ref name="WHO rejects rumours">{{cite news|title=WHO rejects polio rumours|url=http://dawn.com/2012/02/26/who-rejects-polio-rumours/|accessdate=3 June 2012|newspaper=Dawn|date=26 February 2012|author=Imran Ali Teepu}}</ref>  Even with the express support of political leaders, polio workers or their accompanying security guards have been kidnapped, beaten, or assassinated.<ref name="Religious opposition">{{cite journal |author=Warraich HJ |title=Religious opposition to polio vaccination |journal=Emerg Infect Dis |volume=15 |issue=6 |doi=10.3201/eid1506.090087 |url=http://cdc.gov/eid/content/15/6/978a.htm |year= 2009 |pmc=2727330 |page=978 |pmid=19523311}}</ref> 

Polio vaccination efforts have also faced resistance in another form. The priority placed on vaccination by national authorities has turned it into a bargaining chip, with communities and interest groups resisting vaccination, not due to direct opposition, but to leverage other concessions from governmental authorities. In Nigeria this has taken the form of 'block rejection' of vaccination that is only resolved when state officials agree to repair or improve schools and health-care facilities, pave roads or install electricity.<ref>{{cite news|title=Polio is back in Nigeria, and the next vaccination campaign may have a surprising consequence|author1=Shelby Grossman, Jonathan Phillips  |author2=Leah Rosenzweig|url=https://www.washingtonpost.com/news/monkey-cage/wp/2016/08/23/polio-is-back-in-nigeria-heres-why-local-communities-will-bargain-hard-on-the-next-vaccination-surge/|newspaper=Washington Post|date=23 August 2016|accessdate=23 August 2016}}</ref> There have been several instances of threatened boycotts by health workers in Pakistan over payment disputes.<ref>{{cite news|title=Protesting health workers threaten to boycott anti-polio drive|author=Dawn|url=http://www.dawn.com/news/1205076|newspaper=Dawn|date=5 September 2015|accessdate=23 August 2016}}</ref><ref>{{cite news|title=Up in arms: EPI workers threaten to boycott polio drives in FATA|author=Express Tribune|url=http://tribune.com.pk/story/1091625/up-in-arms-epi-workers-threaten-to-boycott-polio-drives-in-fata/|newspaper=Express Tribune|date=26 April 2016|accessdate=23 August 2016}}</ref>  Some governments have been accused of withholding vaccination or the necessary accompanying infrastructure from regions where opposition to their rule is high.<ref>{{cite web|last=Sparrow|first=Annie|title=Syria’s Polio Epidemic: The Suppressed Truth|date=20 February 2014|accessdate=31 August 2018|publisher=The New York Review of Books|url=https://www.nybooks.com/articles/2014/02/20/syrias-polio-epidemic-suppressed-truth/}}</ref>

== Polio eradication criteria ==
A country is regarded as polio free or non-endemic if no cases have been detected for a year.<ref>{{Cite web|url=http://www.who.int/mediacentre/news/releases/2015/nigeria-polio/en/|title=WHO {{!}} WHO Removes Nigeria from Polio-Endemic List|website=www.who.int|access-date=2017-10-10}}</ref><ref name=":2" /> However, it is still possible polio circulates under these circumstances, as was the case for Nigeria, where a particular strain of virus resurfaced after five years in 2016.<ref>{{Cite news|url=http://www.who.int/news-room/detail/11-08-2016-government-of-nigeria-reports-2-wild-polio-cases-first-since-july-2014|title=Government of Nigeria reports 2 wild polio cases, first since July 2014|work=World Health Organization|access-date=2018-08-25|language=en-US}}</ref> This can be due to chance, limited surveillance and under-vaccinated populations.<ref name=":3">{{Cite journal|last=McCarthy|first=Kevin A.|last2=Chabot-Couture|first2=Guillaume|last3=Shuaib|first3=Faisal|date=2016-09-29|title=A spatial model of Wild Poliovirus Type 1 in Kano State, Nigeria: calibration and assessment of elimination probability|url=https://doi.org/10.1186/s12879-016-1817-3|journal=BMC Infectious Diseases|volume=16|pages=521|doi=10.1186/s12879-016-1817-3|issn=1471-2334}}</ref> Moreover, for the currently circulating virus WPV1, only 1 in 200 infection cases exhibit symptoms of polio paralysis in non-vaccinated children, and possibly even fewer in vaccinated children.<ref name="Kalkowska 66">{{Cite journal|last=Kalkowska|first=Dominika A.|last2=Duintjer Tebbens|first2=Radboud J.|last3=Pallansch|first3=Mark A.|last4=Cochi|first4=Stephen L.|last5=Wassilak|first5=Steven G. F.|last6=Thompson|first6=Kimberly M.|date=2015-02-18|title=Modeling undetected live poliovirus circulation after apparent interruption of transmission: implications for surveillance and vaccination|url=https://doi.org/10.1186/s12879-015-0791-5|journal=BMC Infectious Diseases|volume=15|pages=66|doi=10.1186/s12879-015-0791-5|issn=1471-2334}}</ref> Therefore, even a single case is considered an epidemic.<ref>{{Cite web|url=https://www.cgdev.org/doc/millions/MS_case_5.pdf|title=Case 5: Eliminating Polio in Latin America and the Caribbean|last=|first=|date=|website=|access-date=2017-10-10}}</ref> According to modeling, it can take four to six months of no reported cases to achieve only a 50% chance of eradication, and one to two years for e.g. 95% chance.<ref name=":3" /><ref name="Kalkowska 66"/> Sensitivity of monitoring for circulation can be improved by sampling sewage. In Pakistan in the last couple of years, the number of paralysis cases has dropped relatively faster than the positive environmental samples. The presence of multiple infections with the same strain in the upstream area may not be detectable, so there are some saturation effects when monitoring the number of positive environmental samples.<ref>{{Cite web|url=http://polioeradication.org/polio-today/polio-now/surveillance-indicators/|title=GPEI-Surveillance Indicators|website=polioeradication.org|language=en-GB|access-date=2018-03-25}}</ref><ref>{{Cite journal|last=Cowger|first=Tori L.|last2=Burns|first2=Cara C.|last3=Sharif|first3=Salmaan|last4=Jr|first4=Howard E. Gary|last5=Iber|first5=Jane|last6=Henderson|first6=Elizabeth|last7=Malik|first7=Farzana|last8=Zaidi|first8=Syed Sohail Zahoor|last9=Shaukat|first9=Shahzad|date=2017-07-25|title=The role of supplementary environmental surveillance to complement acute flaccid paralysis surveillance for wild poliovirus in Pakistan – 2011–2013|url=http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0180608|journal=PLOS ONE|language=en|volume=12|issue=7|pages=e0180608|doi=10.1371/journal.pone.0180608|issn=1932-6203|bibcode=2017PLoSO..1280608C}}</ref><ref>{{Cite news|url=http://www.sciencemag.org/news/2018/01/what-hell-going-polio-cases-are-vanishing-pakistan-yet-virus-wont-go-away|title=‘What the hell is going on?’ Polio cases are vanishing in Pakistan, yet the virus won't go away|date=2018-01-11|work=Science {{!}} AAAS|access-date=2018-03-25|language=en}}</ref> Furthermore, virus may shed beyond the expected duration of several weeks in certain individuals.  Contagiousness can not be readily excluded.<ref>{{Cite news|url=http://www.iflscience.com/health-and-medicine/man-has-been-shedding-polio-virus-28-years/|title=This Man Has Been Shedding The Polio Virus For 28 Years|work=IFLScience|access-date=2018-03-25|language=en}}</ref>  For a polio virus to be certified as eradicated worldwide, at least three years of good surveillance without cases needs to be achieved,<ref>{{cite news|last=Miles|first=Tom|title=WHO experts signal victory over one of three polio strains|publisher=Reuters.com|url=https://www.reuters.com/article/us-health-polio/who-experts-signal-victory-over-one-of-three-polio-strains-idUSKCN0SH27620151023|date=2015-10-23|access-date=2017-10-10}}</ref> though this period may need to be longer for a strain like WPV3, where a lower proportion of those infected demonstrate symptoms, or if sewer samples stay positive.<ref name="GCC">{{cite report|title=Global Commission for the Certification of Poliomyelitis Eradication (GCC) Report from the Sixteenth Meeting|publisher=Global Commission for the Certification of Poliomyelitis Eradication|date=September 2017|url=http://polioeradication.org/wp-content/uploads/2017/09/GCC-16th-meeting-report-0405072017.pdf}}</ref>  Wild poliovirus type 2 was certified eradicated in 2015, the last case having been detected in 1999.<ref>{{cite web|url=http://polioeradication.org/news-post/global-eradication-of-wild-poliovirus-type-2-declared/|title=Global Eradication of Wild Poliovirus Type 2 Declared|website=polioeradication.org|date=2015-09-20|access-date=2017-10-10}}</ref>  Wild poliovirus type 3 has not been detected since 2012, but its eradication has yet to be certified, and the Global Commission for the Certification of Poliomyelitis Eradication in 2017 recommended not certifying its eradication independent of that of WPV1, and hence of wild poliovirus as a whole.<ref name="GCC" />  This recommendation would mean that type WPV3 will not be removed from the bivalent oral vaccine, as was considered necessary with WPV2 due to its high risk of giving rise to cVDPV strains, but rather oral vaccination for WPV3 will continue until total eradication of polio allows all oral vaccination to cease.

== Timeline ==
{| class="wikitable" style="float:right; font-size:85%; margin-left:15px"
| colspan=3|'''International wild poliovirus cases by year'''
|-
! Year !! Estimated{{Efn|Due to the large increase in the number of vaccinators and field workers since 1998, the number of estimated cases is thought to be reasonably close to the actual reported number of cases in recent years.<ref name="Aylward_2005"/>{{Failed verification|date=January 2018}}}} !! Recorded
|-
| '''1975''' || — || 49,293<ref name="Watch" />
|-
| colspan=3 align="center"| ...
|-
| '''1980''' || 400,000<ref name=":4">{{cite web|url=http://www.unicef.org/pon95/heal0002.html|title=Ending polio—now or never?|last=Lee|first=Jong Wook|year=1995|work=The Progress of Nations|publisher=Unicef|accessdate=2 February 2007}}</ref> || 52,552<ref name="Watch" />
|-
| colspan=3 align="center"| ...
|-
| '''1985''' || — || 38,637<ref name="Watch" />
|-
| colspan=3 align="center"| ...
|-
| 1988 || 350,000<ref name="Aylward_2005">{{cite web|url=http://www.who.int/bulletin/volumes/83/4/268.pdf#search=%222005%20%22%20estimated%20polio%20cases%22%22|title=Polio Eradication:mobilizing and managing the human resources|author1=R. Bruce Aylward|author2=Jennifer Linkins|publisher=World Health Organization|accessdate=29 October 2016}}</ref> || 35,251<ref name="Watch" />
|-
| colspan=3 align="center"| ...
|-
| '''1990''' || — || 23,484<ref name="Watch" />
|-
| colspan=3 align="center"| ...
|-
| 1993 || 100,000<ref name=":4" /> || 10,487<ref name="Watch" />
|-
| colspan=3 align="center"| ...
|-
| '''1995''' || — || 7,035<ref name="Watch" />
|-
| colspan=3 align="center"| ...
|-
| '''2000''' || — || 719<ref name=":5">{{cite web|url=https://extranet.who.int/polis/public/CaseCount.aspx|title=AFP/Polio Case Count|date=6 January 2015|publisher=[[Organization:World Health Organization|World Health Organization]]|accessdate=10 January 2015}}</ref>
|-
| colspan=3 align="center"| ...
|-
| '''2005''' || — || 1,979<ref name=":5" />
|-
| colspan=3 align="center"| ...
|-
| '''2010''' || — || 1,352<ref name=":5" />
|-
| 2011 || — || 650<ref name=":5" />
|-
| 2012 || — || 223<ref name=":5" />
|-
| 2013 || — || 416<ref name=":5" />
|-
| 2014 || — || 359<ref name=":5" />
|-
| '''2015''' || — || 74<ref name=":5" />
|-
|2016
|—
|37<ref name=":5" />
|-
|2017
|—
|22<ref name=":6" />
|}

=== Pre-1988 ===
[[File:Number of poliovirus cases by year.png|right|thumb|300px|Number of poliovirus cases by year, 1975–2017]]
Following the widespread use of poliovirus vaccine in the mid-1950s, the incidence of poliomyelitis declined rapidly in many industrialized countries.<ref name= PinkBook/> [[Place:Czechoslovakia|Czechoslovakia]] became the first country in the world to scientifically demonstrate nationwide eradication of poliomyelitis in 1960.<ref>{{cite journal |author=Slonim D |title=Global eradication of poliomyelitis. On the 80th anniversary of the founding of the National Institute of Health |journal=Epidemiol Mikrobiol Imunol |volume=54 |issue=3 |pages=99–108 |year=2005 |pmid=16173520}}</ref> In 1962—just one year after Sabin's oral polio vaccine (OPV) was licensed in most industrialized countries—Cuba began using the oral vaccine in a series of nationwide polio campaigns. The early success of these mass vaccination campaigns suggested that polioviruses could be globally eradicated.<ref name= Hinman>{{cite journal |author=Hinman A |title=Landmark perspective: Mass vaccination against polio |journal=JAMA |volume=251 |issue=22 |pages=2994–6 |year=1984 |pmid = 6371280 |doi=10.1001/jama.1984.03340460072029}}</ref> The Pan American Health Organization (PAHO), under the leadership of Ciro de Quadros, launched an initiative to eradicate polio from the [[Earth:Americas|Americas]] in 1985.<ref name= Fujimura>{{cite web| author = Fujimura SF | title = The Man Who Made Polio History |publisher = Pan American Health Organization | year = 2005 | url = http://www.paho.org/English/DD/PIN/Number22_article2.htm | accessdate = 2 February 2007 }}</ref>

Much of the work towards eradication was documented by Brazilian photographer Sebastião Salgado, as a UNICEF Goodwill Ambassador, in the book ''The End of Polio: Global Effort to End a Disease''.<ref>{{cite press release | title = The End of Polio: Photographs of Sebastião Salgado Opens to Public | url =https://www.cdc.gov/media/pressrel/2007/r070824.htm | date = 24 August 2007 | accessdate = 2 June 2008 | publisher = Centers for Disease Control and Prevention}}</ref>

=== 1988–2000 ===

In 1988, the [[Organization:World Health Organization|World Health Organization]], together with Rotary International, UNICEF, and the U.S. Centers for Disease Control and Prevention passed the [[Organization:Global Polio Eradication Initiative|Global Polio Eradication Initiative]], with the goal of eradicating polio by the year 2000. The initiative was inspired by Rotary International's 1985 pledge to raise $120 million toward immunising all of the world's children against the disease.<ref name= Fujimura/> The last case of [[Biology:Wild type|wild]] poliovirus poliomyelitis in the Americas was reported in Peru, August 1991.<ref name= Fujimura/>

On 20 August 1994 the Americas were certified as polio-free.<ref name=MMWR_1994>{{cite journal| title = International Notes Certification of Poliomyelitis Eradication&nbsp;– the Americas, 1994 | journal = Morbidity and Mortality Weekly Report | publisher = Centers for Disease Control and Prevention | volume= 43 | issue= 39 | pages = 720–722 | year=1994 | url = https://www.cdc.gov/mmwr/preview/mmwrhtml/00032760.htm | pmid = 7522302| author1= Centers for Disease Control and Prevention (CDC) }}</ref> This achievement was a milestone in efforts to eradicate the disease.

In 1994 the Indian Government launched the Pulse Polio Campaign to eliminate polio. The current campaign involves annual vaccination of all children under age five.<ref>{{cite web| title = Pulse Polio Programme |publisher = Government of India; Department of Family Welfare | year = 2013 | url = http://www.chaloafrica.com/wp-content/uploads/2014/06/pulse-polio-programme.pdf | accessdate = 10 July 2014 }}</ref>

In 1995 Operation MECACAR (Mediterranean, [[Earth:Caucasus|Caucasus]], Central Asian Republics and {{wipe|Russia}}) were launched; National Immunization Days were coordinated in 19 [[Earth:Europe|Europe]]an and Mediterranean countries.<ref>{{cite web| title = Operation MECACAR |publisher = WHO Regional office for Europe | date = 2 June 2006 | url = http://www.euro.who.int/vaccine/20030724_13 | accessdate = 2 February 2007 |archiveurl = https://web.archive.org/web/20070729061315/http://www.euro.who.int/vaccine/20030724_13 <!-- Bot retrieved archive --> |archivedate = 29 July 2007}}</ref> In 1998, Melik Minas of [[Place:Turkey|Turkey]] became the last case of polio reported in Europe.<ref>{{cite web|title=WHO European Region celebrates three polio-free years: certification within reach in 2002 |author=WHO Regional Office for Europe |work=Press release 13/2001 |url=http://www.euro.who.int/mediacentre/PR/2001/20011217_3 |date=30 November 2001 |accessdate=31 July 2007 |deadurl=yes |archiveurl=https://web.archive.org/web/20050922102347/http://www.euro.who.int/mediacentre/pr/2001/20011217_3 |archivedate=22 September 2005 }}</ref> In 1997 Mum Chanty of Cambodia became the last person to contract polio in the Indo-West Pacific region.<ref name=Pacific>{{cite journal | author1 = Yamazaki, S. | author2 = Toraya, H.| title = (General News) Major Milestone reached in Global Polio Eradication: Western Pacific Region is certified Polio-Free | journal = Health Educ. Res. | year = 2001 | volume = 16 | pages = 110–114 | url = http://her.oxfordjournals.org/cgi/reprint/16/1/109.pdf | issue = 1 | doi = 10.1154/1.1351153 | bibcode = 2001PDiff..16..110Y}}</ref> In 2000 the Western Pacific Region (including {{wipe|China}}) was certified polio-free.<ref name=Pacific />

In October 1999, the last isolation of type 2 poliovirus occurred in India. This type of poliovirus was declared eradicated.<ref name= PinkBook/><ref name="News stories">{{Cite web|title = News stories|url = http://www.polioeradication.org/mediaroom/newsstories/Global-eradication-of-wild-poliovirus-type-2-declared/tabid/526/news/1289/Default.aspx|website = www.polioeradication.org|accessdate = 27 September 2015}}</ref>

Also in October 1999, The CORE Group—with funding from the United States Agency for International Development (USAID)—launched its effort to support national eradication efforts at the grassroots level. The CORE Group initiated this initiative in Bangladesh, India and Nepal in South Asia, and in Angola, Ethiopia and Uganda in Africa.<ref>{{cite web|title=CORE Group Polio Eradication Initiative |url=http://www.coregroup.org/initiatives/polio.cfm |accessdate=10 March 2009 |deadurl=yes |archiveurl=https://web.archive.org/web/20090227134640/http://www.coregroup.org/initiatives/polio.cfm |archivedate=27 February 2009 }}</ref>

=== 2001–2005 ===
[[File:Poliomyelitis world map - DALY - WHO2004.svg|thumb|[[Disability-adjusted life year]] for poliomyelitis per 100,000&nbsp;inhabitants in 2004
{{Col-begin}}
{{Col-break}}
{{legend|#b3b3b3|no data}}
{{legend|#ffff65|<0.3}}
{{legend|#fff200|0.3–0.75}}
{{legend|#ffdc00|0.75–1.2}}
{{legend|#ffc600|1.2–1.65}}
{{legend|#ffb000|1.65–2.1}}
{{legend|#ff9a00|2.1–2.55}}
{{Col-break}}
{{legend|#ff8400|2.55–3}}
{{legend|#ff6e00|3–4}}
{{legend|#ff5800|4–5}}
{{legend|#ff4200|5–7.5}}
{{legend|#ff2c00|7.5–10}}
{{legend|#cb0000|>10}}
{{col-end}}]]

By 2001, 575 million children (almost one-tenth the world's population) had received some 2 billion doses of oral polio vaccine.<ref name=Rotary.Timeline>{{cite web|title=PolioPlus Timeline |publisher=Rotary International |url=http://www.rotary.org/en/serviceandfellowship/polio/timeline/Pages/ridefault.aspx |accessdate=11 March 2011 |deadurl=yes |archiveurl=https://web.archive.org/web/20110220222008/http://www.rotary.org/en/ServiceAndFellowship/Polio/Timeline/Pages/ridefault.aspx |archivedate=20 February 2011 }}</ref> The World Health Organization announced that Europe was polio-free on 21 June 2002, in the [[Place:Copenhagen|Copenhagen]] Glyptotek.<ref>{{cite news | title = Europe achieves historic milestone as Region is declared polio-free | work = Press release | pages = | publisher = European Region of the World Health Organization | date = 21 June 2002 | url = http://www.euro.who.int/mediacentre/PR/2002/20020620_1 | archiveurl=https://web.archive.org/web/20100516220858/http://www.euro.who.int/mediacentre/PR/2002/20020620_1 | archivedate=16 May 2010 | accessdate = 2 February 2007 }}</ref>

In 2002, an outbreak of polio occurred in India. The number of planned polio vaccination campaigns had recently been reduced, and populations in northern India, particularly from the Islamic background, engaged in mass resistance to immunization. At this time, the Indian state Uttar Pradesh accounted for nearly two-thirds of total worldwide cases reported.<ref>{{cite web | title = WHO Director-General calls India 'number 1' polio eradication priority | work = News release | url = http://www.who.int/mediacentre/news/releases/2003/pr30/en/index.html | date = 7 April 2003 | accessdate = 31 July 2007}}</ref> (See the [[:Image:Poliokarte-Dezember-2002.jpg|2002 Global polio incidence map]].) However, by 2004, India had adopted strategies to increase ownership of polio vaccinations in marginalized populations, and the immunity gap in vulnerable groups rapidly closed.{{citation needed|date=May 2017}}

In August 2003, rumors spread in some states in Nigeria, especially Kano, that the vaccine caused sterility in girls. This resulted in the suspension of immunization efforts in the state, causing a dramatic rise in polio rates in the already endemic country.<ref name="Jegede2007">{{cite journal |last1=Jegede |first1=A. S. |year= 2007|title=What Led to the Nigerian Boycott of the Polio Vaccination Campaign? |journal=PLoS Medicine |volume=4 |issue=3 |page=e73 |doi=10.1371/journal.pmed.0040073 |url=http://www.plosmedicine.org/article/info:doi/10.1371/journal.pmed.0040073 |accessdate=1 June 2012 |pmid=17388657 |pmc=1831725}}</ref> On 30 June 2004, the WHO announced that after a 10-month ban on polio vaccinations, Kano had pledged to restart the campaign in early July. During the ban the virus spread across Nigeria and into 12 neighboring countries that had previously been polio-free.<ref name= Fujimura/> By 2006, this ban would be blamed for 1,500 children being paralyzed and had cost $450 million for emergency activities. In addition to the rumors of sterility and the ban by Nigeria's Kano state, civil war and internal strife in the Sudan and Côte d'Ivoire have complicated WHO's polio eradication goal. In 2004, almost two-thirds of all the polio cases in the world occurred in Nigeria (760 out of 1,170 total).{{citation needed|date=May 2017}}[[File:Polio worldwide 2005.svg|thumb|right|200px|Countries with polio cases in 2005]]

In May 2004 the first case of the polio outbreak in Sudan was detected. The reemergence of polio led to stepped up vaccination campaigns. In the city of Darfur, 78,654 children were immunized and 20,432 more in southern Sudan (Yirol and Chelkou).<ref>{{cite news|url=http://www.noticias.info/Archivo/2005/200505/20050511/20050511_65088.shtm|title=Sudan: Bulletin No. 28|date=11 May 2005|work=International Committee of the Red Cross (ICRC)|accessdate=7 February 2007}}</ref>

In 2005 there were 1,979 cases of wild poliovirus (excludes [[Biology:Vaccine|vaccine]]-derived polio [[Biology:Virus|virus]]es).<ref name=":0">{{Cite web|url = http://www.polioeradication.org/Portals/0/Document/Data&Monitoring/Wild_poliovirus_list_2005_2011_03Jan.pdf|title = Wild Poliovirus List 2005-2011|date = 3 January 2012|accessdate = 13 September 2015|website = Global Polio Eradication Initiative|publisher = }}</ref> Most cases were located in two areas: the [[Earth:Indian subcontinent|Indian subcontinent]] and Nigeria. Eradication efforts in the Indian sub-continent met with a large measure of success. Using the Pulse Polio campaign to increase polio immunization rates, {{wipe|India}} recorded just 66 cases in 2005, down from 135 cases reported in 2004, 225 in 2003, and 1,600 in 2002.<ref name=WHO.2014>{{cite web| title = WHO Vaccine Preventable Diseases: Monitoring system |publisher = World Health Organization | year = 2014 | url = http://www.who.int/entity/immunization_monitoring/data/incidence_series.xls | accessdate = 21 October 2014|format=XLS}}</ref>

Yemen, Indonesia and Sudan, countries that had been declared polio-free since before 2000, each reported hundreds of cases—probably imported from Nigeria.<ref name=Nigeria>{{cite news | author = Balint-Kurti D | title = Polio Spreads From Nigeria After Claims | agency=Associated Press | date = 4 May 2005 | url=http://www.ar15.com/archive/topic.html?b=1&f=5&t=348684 | accessdate = 19 January 2013}}</ref> On 5 May 2005, news reports broke that a new case of polio was diagnosed in Java, Indonesia, and the virus strain was suspected to be the same as the one that has caused outbreaks in Nigeria. New public fears over vaccine safety, which were unfounded, impeded vaccination efforts in Indonesia. In summer 2005 the WHO, UNICEF and the Indonesian government made new efforts to lay the fears to rest, recruiting celebrities and religious leaders in a publicity campaign to promote vaccination.<ref>{{cite news | author = Aglionby J | title =Indonesia faces polio challenge| work = Guardian Unlimited | date = 2 September 2005 | url= https://www.theguardian.com/elsewhere/country/story/0,7792,1561473,00.html | accessdate = 7 February 2007}}</ref>

In the {{wipe|United States}} on 29 September 2005, the Minnesota Department of Health identified the first occurrence of vaccine derived polio virus (VDPV) transmission in the United States since OPV was discontinued in 2000. The poliovirus type 1 infection occurred in an unvaccinated, immunocompromised infant girl aged 7 months (the index patient) in an Amish community whose members predominantly were not vaccinated for polio.<ref name="Bahta_2005">{{cite journal |vauthors=Bahta L, etal |title=Poliovirus infections in four unvaccinated children—Minnesota, August–October 2005 |journal=MMWR Morb Mortal Wkly Rep |volume=54 |issue=41 |pages=1053–5 |year=2005 |url=https://www.cdc.gov/mmwr/preview/mmwrhtml/mm5441a6.htm | pmid = 16237378}}</ref>

=== 2006–2010 ===

In 2006 only four countries in the world (Nigeria, India, {{wipe|Pakistan}} and Afghanistan) were reported to have endemic polio. Cases in other countries are attributed to importation. A total of 1,997 cases worldwide were reported in 2006; of these the majority (1,869 cases) occurred in countries with endemic polio.<ref name=":0" /> Nigeria accounted for the majority of cases (1,122 cases) but India reported more than ten times more cases this year than in 2005 (676 cases, or 30% of worldwide cases). Pakistan and Afghanistan reported 40 and 31 cases respectively in 2006. Polio re-surfaced in Bangladesh after nearly six years of absence with 18 new cases reported. "Our country is not safe, as neighbours India and Pakistan are not polio free", declared Health Minister ASM Matiur Rahman.<ref name="BBC World">{{cite news | title = Bangladesh begins new polio drive | url = http://news.bbc.co.uk/2/hi/south_asia/6412835.stm | work = BBC News | publisher = | date = 2 March 2007 | accessdate = 31 July 2007}}</ref> (See: [[:Image:Poliomyelite.png|Map of reported polio cases in 2006]])

In 2007 there were 1,315 cases of poliomyelitis reported worldwide.<ref name=":0" /> Over 60% of cases (874) occurred in India; while in Nigeria, the number of polio cases fell dramatically, from 1,122 cases reported in 2006 to 285 cases in 2007. Officials credit the drop in new infections to improved political control in the southern states and resumed immunisation in the north, where Muslim clerics led a boycott of vaccination in late 2003. Local governments and clerics allowed vaccinations to resume on the condition that the vaccines be manufactured in Indonesia, a majority Muslim country, and not in the United States.<ref name=Nigeria/> Turai Yar'Adua, wife of recently elected Nigerian president Umaru Yar'Adua, made the eradication of polio one of her priorities. Attending the launch of immunization campaigns in Birnin Kebbi in July 2007, Turai Yar'Adua urged parents to vaccinate their children and stressed the safety of oral polio vaccine.<ref>{{cite web |url=http://www.polioeradication.org/content/general/LatestNews200707.asp |title=First Lady of Nigeria inaugurates vaccination campaigns |accessdate=24 January 2008 |date=30 July 2007 |work=The Global Polio Eradication Initiative |archiveurl = https://web.archive.org/web/20071209001901/http://www.polioeradication.org/content/general/LatestNews200707.asp <!-- Bot retrieved archive --> |archivedate = 9 December 2007}}</ref>

In July 2007, a student traveling from Pakistan imported the first polio case to {{wipe|Australia}} in over 20 years.<ref>{{cite news | author = Yusufzai A | title = Pakistan polio case in Australia | publisher = BBC News | date = 30 July 2007 | accessdate = 8 August 2007 | url = http://news.bbc.co.uk/2/hi/south_asia/6922991.stm}}</ref> Other countries with significant numbers of wild polio virus cases include the Democratic Republic of the Congo, which reported 41 cases, Chad with 22 cases, and Niger and Myanmar, each of which reported 11 cases.<ref name=":0" />

In 2008, 19 countries reported cases and the total number of cases was 1,652. Of these, 1,506 occurred in the four endemic countries and 146 elsewhere. The largest number were in Nigeria (799 cases) and India (559 cases): these two countries contributed 82.2 percent of all cases. Outside endemic countries Chad reported the greatest number (37 cases).<ref name=":0" />

In 2009, a total of 1,606 cases were reported in 23 countries. Four endemic countries accounted for 1,256 of these, with the remaining 350 in 19 sub-Saharan countries with imported cases or re-established transmission. Once again, the largest number were in India (741) and Nigeria (388).<ref name=":0" /> All other countries had less than one hundred cases: Pakistan had 89 cases, Afghanistan 38, Chad 65, Sudan 45, Guinea 42, Angola 29, Côte d'Ivoire 26, Benin 20, Kenya 19, Niger 15, Central African Republic 14, Mauritania 13 and Sierra Leone and Liberia both had 11. The following countries had single digit numbers of cases: Burundi 2, Cameroon 3, the Democratic Republic of the Congo 3, Mali 2, Togo 6 and Uganda 8.

According to figures updated in April 2012, the WHO reported that there were 1,352 cases of wild polio in 20 countries in 2010. Reported cases of polio were down 95% in Nigeria (to a historic low of 21 cases) and 94% in India (to a historic low of 42 cases) compared to the previous year, with little change in Afghanistan (from 38 to 25 cases) and an increase in cases in Pakistan (from 89 to 144 cases). An acute outbreak in Tajikistan gave rise to 460 cases (34% of the global total), and was associated with a further 18 cases across Central Asia (Kazakhstan and Turkmenistan) and the Russian Federation, with the most recent case from this region being reported from Russia 25 September. These were the first cases in the WHO European region since 2002. The Republic of Congo ([[Place:Brazzaville|Brazzaville]]) saw an outbreak with 441 cases (30% of the global total). At least 179 deaths were associated with this outbreak, which is believed to have been an importation from the ongoing type 1 outbreak in Angola (33 cases in 2010) and the Democratic Republic of the Congo (100 cases).<ref name=":0" /><ref name="Wildlist01Jan13">{{cite web|url=http://www.polioeradication.org/Portals/0/Document/Data&Monitoring/Wild_poliovirus_list_2007_2012_1Jan.pdf|title=WHO Wild Poliovirus List|last=|first=|date=|website=|archive-url=https://web.archive.org/web/20130518114944/http://polioeradication.org/Portals/0/Document/Data%26Monitoring/Wild_poliovirus_list_2007_2012_1Jan.pdf|archive-date=18 May 2013|dead-url=yes|accessdate=3 February 2013|df=dmy-all}}</ref>

{{clear}}

=== 2011–2015 ===
In 2011, 650 WPV cases were reported in sixteen countries: the four endemic countries—Pakistan, Afghanistan, Nigeria and India—as well as twelve others. Polio transmission recurred in Angola, Chad and the Democratic Republic of the Congo. Kenya reported its first case since 2009, while {{wipe|China}} reported 21 cases, mostly among the Uyghurs of Hotan prefecture, [[Place:Xinjiang|Xinjiang]], the first cases since 1994.{{citation needed|date=July 2018}}

The total number of wild-virus cases reported in 2012 was 223, lower than any previous year. These were limited to five countries—Nigeria, Pakistan, Afghanistan, Chad, and Niger—of which all except Nigeria had fewer cases than in 2011.<ref name=":1" /> Several additional countries, Chad, Democratic Republic of the Congo, Somalia and Yemen, saw outbreaks of circulating vaccine-derived polio. The last reported type 3 case of polio worldwide had its onset 11 November 2012 in Nigeria; the last wild case outside Nigeria was in April 2012 in Pakistan,<ref name=":1" /> and its absence from sewage monitoring in Pakistan suggests that active transmission of this strain has ceased there.<ref>{{cite web|author=Asif Choudary |url=http://dawn.com/2013/01/27/pakistan-close-to-getting-rid-of-a-polio-virus-who/ |title=Pakistan close to getting rid of a polio virus: WHO |publisher=Dawn.com |date=27 January 2013 |accessdate=29 March 2014}}</ref>  A total of 416 wild-virus cases were reported in 2013, almost double the previous year. Of these, cases in endemic countries dropped from 197 to 160, while those in non-endemic countries jumped from 5 to 256 owing to two outbreaks: one in the [[Place:Horn of Africa|Horn of Africa]], and one in [[Place:Syria|Syria]].

In April, a case of wild polio in [[Place:Mogadishu|Mogadishu]] was reported, the first in Somalia since 2007.<ref name="Somalia wild">{{cite web|last=Callaway |first=Ewen |url=http://blogs.nature.com/news/2013/05/somalia-records-its-first-wild-polio-case-since-2007.html |title=Somalia records its first wild polio case since 2007 |work=Nature News Blog |date=13 May 2013 |accessdate=30 September 2015}}</ref> By October, over 170 cases had been reported in the country,<ref>[https://www.bbc.co.uk/news/world-africa-23729121 Polio in Somalia: UN warns of 'explosive' outbreak], BBC News, 16 August 2013</ref> with more cases in neighboring Kenya and the Somali Region of Ethiopia.

Routine sewage monitoring in 2012 had detected a WPV1 strain of Pakistani origin in [[Place:Cairo|Cairo]], sparking a major vaccination push there.<ref>{{cite news|last=McNeil Jr.|first=Donald G.|title=Egypt: Polio Virus Is Found in Cairo’s Sewers|url=https://www.nytimes.com/2013/01/24/health/egypt-polio-virus-is-found-in-cairos-sewers.html?_r=1&|accessdate=28 April 2013|newspaper={{wipe|The New York Times}}|date=23 January 2013}}</ref> The strain spread to Israel, where there was widespread environmental detection, but like Egypt, no paralysis cases.<ref name="polio detected Israel">{{cite web|url=http://www.who.int/csr/don/2013_06_03/en/index.html |title=Poliovirus detected from environmental samples in Israel |agency=World Health Organization |date=3 June 2013 |accessdate=30 September 2015}}</ref><ref name="polio Israel TOI">{{cite news|last1=Sterman|first1=Adiv|last2=Winer Jr.|first2=Stuart|title=More polio virus traces detected in Israel|url=http://www.timesofisrael.com/more-polio-virus-traces-detected-in-israel/|accessdate=13 June 2013|newspaper=Times of Israel|date=12 June 2013}}</ref><ref name="polio Israel NYT">{{cite news|last=McNeil Jr.|first=Donald G.|title=Polio Virus Discovered in Sewage From Israel|url=https://www.nytimes.com/2013/06/04/health/polio-virus-discovered-in-sewage-from-israel.html?_r=0|accessdate=3 June 2013|newspaper={{wipe|The New York Times}}|date=7 June 2013}}</ref> It had more severe consequences when it spread to neighboring Syria, with the total number of cases eventually reaching 35, the first outbreak there since 1999.<ref>[https://www.bbc.co.uk/news/world-middle-east-24726592 Syria polio outbreak confirmed by WHO], BBC News, 29 October 2013</ref><ref name="Syria polio linked Egypt">{{cite news|last=Nebehay, |first=Stephanie|title=Polio strain in Syria originated in Pakistan, WHO confirms|url=http://www.nbcnews.com/health/polio-strain-syria-originated-pakistan-who-confirms-2D11577484|date=11 November 2013|accessdate=12 November 2013|publisher=NBC News}}</ref>

In late April 2013, the WHO announced a new $5.5 billion, 6-year cooperative plan (called the 2013–18 Polio Eradication and Endgame Strategic Plan) to eradicate polio from its last reservoirs. The plan called for mass immunization campaigns in the three remaining endemic countries, and also dictated a switch to inactivated virus injections, to avoid the risk of the vaccine-derived outbreaks that occasionally occur from use of the live-virus oral vaccine.<ref name="5.5 billion">{{cite web|last=Beaubien |first=Jason |url=https://www.npr.org/blogs/health/2013/04/26/178993960/a-5-5-billion-road-map-to-banish-polio-forever |title=A $5.5 Billion Road Map To Banish Polio Forever |agency=National Public Radio |date=26 April 2013 |accessdate=30 September 2015}}</ref>

In 2014, there were 359 reported cases of wild poliomyelitis, spread over twelve countries. Pakistan had the most with 306, an increase from 93 in 2013, which was blamed on Al Qaeda and Taliban militants preventing aid workers from vaccinating children in rural regions of the country.<ref>{{Cite web|url = http://www.cctv-america.com/2014/10/16/number-of-polio-cases-in-pakistan-highest-in-14-years|title = Number of polio cases in Pakistan highest in 14 years|date = 16 October 2014|accessdate = 20 October 2014|website = |publisher = China Central TV|last = Khan|first = Danial}}</ref><ref>{{cite report|title=Semi-Annual Status Report, January-June 2014|publisher=Global Polio Eradication Initiative|url=http://polioeradication.org/wp-content/uploads/2016/07/GPEI_StatusReport2014Jan-Jun.pdf | access-date=11 June 2018}}</ref><ref>{{cite report|title=Semi-Annual Status Report, July-December 2014|publisher=Global Polio Eradication Initiative|url=http://polioeradication.org/wp-content/uploads/2016/07/GPEI_StatusReport2014Jul-Dec.pdf| access-date=11 June 2018}}</ref>  On 27 March 2014, the WHO announced the eradication of poliomyelitis in the South-East Asia Region, in which the WHO includes eleven countries: Bangladesh, Bhutan, North Korea, {{wipe|India}}, Indonesia, [[History:Maldives|Maldives]], Myanmar, Nepal, Sri Lanka, Thailand and Timor-Leste.<ref name="eradication">{{cite web | url =http://www.searo.who.int/mediacentre/releases/2014/pr1569/en/| title =WHO South-East Asia Region certified polio-free|publisher =WHO|date=27 March 2014| accessdate =27 March 2014}}</ref> With the addition of this region, the proportion of world population living in polio-free regions reached 80%.<ref name="eradication" /> The last case of wild polio in the South-East Asia Region was reported in India on 13 January 2011.<ref>{{cite web | url =http://www.searo.who.int/entity/immunization/topics/polio/eradication/sea-polio-free/en/| title =Polio-free certification: WHO South-East Asia |publisher =WHO|date=27 March 2014| accessdate =27 March 2014}}</ref>

During 2015, 74 cases of wild poliomyelitis were reported worldwide, 54 in Pakistan and 20 in Afghanistan. There were 32 circulating vaccine-derived poliovirus (cVDPV) cases in 2015.<ref>{{cite report|title=Semi-Annual Status Report, January-June 2015|publisher=Global Polio Eradication Initiative|url=http://polioeradication.org/wp-content/uploads/2016/07/GPEI_StatusReport2015Jan-Jun.pdf | access-date=11 June 2018}}</ref><ref>{{cite report|title=Semi-Annual Status Report, July-December 2015|publisher=Global Polio Eradication Initiative|url=http://polioeradication.org/wp-content/uploads/2016/07/GPEI_StatusReport2015Jul-Dec-2.pdf| access-date=11 June 2018}}</ref>

On 25 September 2015, the WHO declared that Nigeria was no longer considered endemic for wild polio virus,<ref>{{Cite web|title = WHO {{!}} WHO Removes Nigeria from Polio-Endemic List|url = http://www.who.int/mediacentre/news/releases/2015/nigeria-polio/en/|website = www.who.int|accessdate = 27 September 2015}}</ref> with no reported case of wild polio virus having been reported since 24 July 2014.<ref name=":1">{{Cite web|url=http://www.polioeradication.org/Portals/0/Document/Data&Monitoring/Wild_poliovirus_list_2010-2015_8SEP.pdf|title=Wild Poliovirus 2010–2015|last=|first=|date=9 September 2015|website=Global Polio Eradication Initiative|publisher=|archive-url=https://web.archive.org/web/20150928032436/http://polioeradication.org/Portals/0/Document/Data%26Monitoring/Wild_poliovirus_list_2010-2015_8SEP.pdf|archive-date=28 September 2015|dead-url=yes|accessdate=12 September 2015|df=dmy-all}}</ref>  A WPV1 strain not seen in 5 years resurfaced in Nigeria the following year.<ref>{{Cite news|url=http://www.who.int/news-room/detail/11-08-2016-government-of-nigeria-reports-2-wild-polio-cases-first-since-july-2014|title=Government of Nigeria reports 2 wild polio cases, first since July 2014|work=World Health Organization|access-date=2018-08-25|language=en-US}}</ref>

WPV2 was declared eradicated in September 2015 as it has not been seen since 1999 and WPV3 may be eradicated as it has not been seen since 2012. cVDPV type 2 was still causing paralysis in some countries due to a years-long evolution in under-immunized populations.<ref name="News stories"/>
{| class="wikitable mw-collapsible mw-collapsed" style="float:right; font-size:85%; margin-left:15px"
| colspan=4 |<div style="text-align: center;">'''Reported polio cases in 2011'''<ref name="WHO2014" />
[[File:Polio worldwide 2011.svg|thumb|center]]</div>
|-
! Country !! Wild<br />cases !! Circulating<br />vaccine-<br />derived<br />cases !! Transmission<br />status
|-
| {{flag|Pakistan}} || 198 || 0 || {{color|#f00|endemic}}
|-
| {{flag|Chad}} || 132 || 0 || {{color|#FF7F00|re-established}}
|-
| {{flag|Democratic Republic of the Congo|name=DRC}} || 93 || 11 || {{color|green|importation}}
|-
| {{flag|Afghanistan}} || 80 || 1 ||{{color|#f00|endemic}}
|-
| {{flag|Nigeria}} || 62 || 33 || {{color|#f00|endemic}}
|-
| {{flag|Côte d'Ivoire}} || 36 || 0 || {{color|green|importation}}
|-
| {{flag|China}} || 21 || 0 || {{color|green|importation}}
|-
| {{flag|Mali}} || 7 || 0 || {{color|green|importation}}
|-
| {{flag|Angola}} || 5 || 0 || {{color|#FF7F00|re-established}}
|-
| {{flag|Niger}} || 5 || 1 || {{color|green|importation}}
|-
| {{flag|Central African Republic}} || 4 || 0 || {{color|green|importation}}
|-
|{{flag|Guinea}} || 3 || 0 || {{color|green|importation}}
|-
|{{flag|Republic of the Congo}} || 1 || 0 || {{color|green|importation}}
|-
| {{flag|Gabon}} || 1 || 0 || {{color|green|importation}}
|-
| {{flag|India}} || 1 || 0 || {{color|#f00|endemic}}
|-
| {{flag|Kenya}} || 1 || 0 || {{color|green|importation}}
|-
| {{Flag|Somalia}} || 0 || 9 || {{color|#00f|cVDPV only}}
|-
| {{flag|Yemen}} || 0 || 9 || {{color|#00f|cVDPV only}}
|-
| {{flag|Mozambique}} || 0 || 2 || {{color|#00f|cVDPV only}}
|-
| '''Total''' || 650 || 66 ||
|}
{| class="wikitable mw-collapsible mw-collapsed" style="float:right; font-size:85%; margin-left:15px"
| colspan=4 |<div style="text-align: center;">'''Reported polio cases in 2012'''<ref name="WHO2014" />
[[File:Polio worldwide 2012.svg|thumb|center]]</div>
|-
! Country !! Wild<br />cases !! Circulating<br />Vaccine-<br />derived<br />cases !! Transmission<br />Status
|-
| {{flag|Nigeria}} || 122 || 9 || {{color|#f00|endemic}}
|-
| {{flag|Pakistan}} || 58 || 16 || {{color|#f00|endemic}}
|-
| {{flag|Afghanistan}} || 37 || 9 || {{color|#f00|endemic}}
|-
| {{flag|Chad}} || 5 || 12 || {{color|#FF7F00|re-established}}
|-
| {{flag|Niger}} || 1 || 0 || {{color|green|importation}}
|-
| {{flag|Democratic Republic of the Congo|name=DRC}}|| 0 || 17 || {{color|#00f|cVDPV only}}
|-
| {{flag|Kenya}} || 0 || 3 || {{color|#00f|cVDPV only}}
|-
| {{flag|Yemen}} || 0 || 2 || {{color|#00f|cVDPV only}}
|-
| {{Flag|China}} || 0 || 2 || {{color|#00f|cVDPV only}}
|-
| {{flag|Somalia}} || 0 || 1 || {{color|#00f|cVDPV only}}
|-
| Total || 223 || 71 ||
|}
{| class="wikitable mw-collapsible mw-collapsed" style="float:right; font-size:85%; margin-left:15px"
| colspan=4 |<div style="text-align: center;">'''Reported polio cases in 2013'''<ref name="WHO2014" />
[[File:Polio worldwide 2013.svg|thumb|center]]</div>
|-
! Country !! Wild<br />cases !! Circulating<br />vaccine-<br />derived<br />cases !! Transmission<br />status
|-
| {{flag|Somalia}} || 194 || 1 || {{color|green|importation}}
|-
| {{flag|Pakistan}} || 93 || 48 || {{color|#f00|endemic}}
|-
| {{flag|Nigeria}} || 53 || 4 || {{color|#f00|endemic}}
|-
| {{flag|Syria}} || 35 || 0 || {{color|green|importation}}
|-
| {{flag|Afghanistan}} || 14 || 3 || {{color|#f00|endemic}}
|-
| {{flag|Kenya}} || 14 || 0 || {{color|green|importation}}
|-
| {{flag|Ethiopia}} || 9 || 0 || {{color|green|importation}}
|-
| {{flag|Cameroon}} || 4 || 4 || {{color|green|importation}}
|-
| {{flag|Chad}} || 0 || 3 || {{color|#00f|cVDPV only}}
|-
|{{Flag|Yemen}} || 0 || 1 || {{color|#00f|cVDPV only}}
|-
| {{flag|Niger}} || 0 || 1 || {{color|#00f|cVDPV only}}
|-
| '''Total''' || 416 || 65 ||
|}
{| class="wikitable mw-collapsible mw-collapsed" style="float:right; font-size:85%; margin-left:15px"
| colspan=4 |<div style="text-align: center;">'''Reported polio cases in 2014'''<ref name="WHO2014" />
</div>[[File:Polio worldwide 2014.svg|thumb|center]]
|-
! Country !! Wild<br />cases !! Circulating<br />vaccine-<br />derived<br />cases !! Transmission<br />status
|-
| {{flag|Pakistan}} || 306 || 22 || {{color|#f00|endemic}}
|-
| {{flag|Afghanistan}} || 28 || 0 || {{color|#f00|endemic}}
|-
| {{flag|Nigeria}} || 6 || 30 || {{color|#f00|endemic}}
|-
| {{flag|Cameroon}} || 5 || 0 || {{color|green|importation}}
|-
| {{flag|Equatorial Guinea}} || 5 || 0 || {{color|green|importation}}
|-
| {{flag|Somalia}} || 5 || 0 || {{color|green|importation}}
|-
| {{flag|Iraq}} || 2 || 0 || {{color|green|importation}}
|-
| {{flag|Ethiopia}} || 1 || 0 || {{color|green|importation}}
|-
| {{flag|Syria}} || 1 || 0 || {{color|green|importation}}
|-
| {{flag|South Sudan}} || 0 || 2 || {{color|#00f|cVDPV only}}
|-
| {{Flag|Guinea}} ||0 || 1 || {{color|#00f|cVDPV only}}
|-
| {{flag|Madagascar}} || 0 || 1 || {{color|#00f|cVDPV only}}
|-
| '''Total''' || 359 || 56 ||
|}
{| class="wikitable mw-collapsible mw-collapsed" style="float:right; font-size:85%; margin-left:15px"
| colspan=5 |<div style="text-align: center;">'''Reported polio cases in 2015'''<ref name="WHO2014" />
[[File:Polio worldwide 2015.svg|thumb|center]]
</div>
|-
! Country !! Wild<br />cases !! Circulating<br />vaccine-<br />derived<br />cases !! Transmission<br />status !! Type(s)
|-
| {{flag|Pakistan}} ||54||2|| {{color|#f00|endemic}} || {{color|#f00|WPV1}}<br />{{color|#00f|cVDPV2}}
|-
| {{flag|Afghanistan}} ||20|| 0 || {{color|#f00|endemic}} || {{color|#f00|WPV1}}
|-
| {{flag|Madagascar}} || 0 || 10 || {{color|#00f|cVDPV only}} || {{color|#00f|cVDPV1}}
|-
| {{flag|Laos}}|| 0 ||8|| {{color|#00f|cVDPV only}} || {{color|#00f|cVDPV1}}
|-
| {{Flag|Guinea}} ||0 || 7 ||{{color|#00f|cVDPV only}} || {{color|#00f|cVDPV2}}
|-
| {{flag|Ukraine}} || 0 || 2 || {{color|#00f|cVDPV only}} || {{color|#00f|cVDPV1}}
|-
| {{flag|Myanmar}} || 0 || 2 ||{{color|#00f|cVDPV only}} || {{color|#00f|cVDPV2}}
|-
| {{flag|Nigeria}} || 0 || 1 ||{{color|#00f|cVDPV only}} || {{color|#00f|cVDPV2}}
|-
| '''Total''' ||74||32|| ||
|}
{{clear}}

=== 2016 ===
{| class="wikitable" style="float:right; font-size:85%; margin-left:15px"
| colspan=5 |<div style="text-align: center;">'''Reported polio cases in 2016'''<ref name="WHO2014" />
[[File:Polio worldwide 2016.svg|thumb|center]]
</div>
|-
! Country !! Wild<br />cases !! Circulating<br />vaccine-<br />derived<br />cases !! Transmission<br />status !! Type(s)
|-
|{{flag|Pakistan}}
|20
|1
|{{color|#f00|endemic}}
|{{color|#f00|WPV1}}<br />{{color|#00f|cVDPV2}}
|-
| {{flag|Afghanistan}} ||13||0|| {{color|#f00|endemic}} || {{color|#f00|WPV1}}
|-
| {{flag|Nigeria}} ||4||1||{{color|#f00|endemic}}||{{color|#f00|WPV1}}<br />{{color|#00f|cVDPV2}}
|-
| {{flag|Laos}} ||0||3||{{color|#00f|cVDPV only}}|| {{color|#00f|cVDPV1}}
|-
| '''Total''' ||37||5|| ||
|}

There were 37 reported WPV1 cases with an onset of paralysis in 2016, half as many as in 2015. Twenty of these cases occurred in Pakistan, thirteen in Afghanistan, and four in Nigeria.<ref>{{cite report|title=Global Polio Eradication Initiative Annual Report 2016|url=http://polioeradication.org/wp-content/uploads/2017/08/AR2016_EN.pdf|access-date=24 June 2018}}</ref> The cases of WPV1 in Nigeria were viewed as a setback, there having been no detected cases caused by the wild virus there in almost two years, yet genetic analysis showed that the virus was of a strain circulating undetected since 2011 in regions inaccessible due to the activities of [[Religion:Boko Haram|Boko Haram]].<ref>{{cite news|author=Judd-Leonard Okafor|title=How polio returned to Nigeria|url=http://www.dailytrust.com.ng/news/general/how-polio-returned-to-nigeria/158649.html|date=11 August 2016|newspaper=Daily Trust|access-date=11 August 2016}}</ref><ref>{{cite news|title=Government of Nigeria reports 2 wild polio cases, first since July 2014|url=http://www.who.int/mediacentre/news/releases/2016/nigeria-polio/en/|date=11 August 2016|newspaper=WHO|access-date=11 August 2016}}</ref>
 	
The 2015 cVDPV1 outbreak in Laos continued into 2016, with three cases in January.<ref>{{Cite web|url=http://www.who.int/csr/don/25-february-2016-polio-lao/en/|title=Circulating vaccine-derived poliovirus – Lao People’s Democratic Republic|website=World Health Organization|language=en-GB|access-date=2017-02-09}}</ref> Two separate strains of cVDPV2 were reported in Nigeria's Borno and Sekoto states, the latter resulting in one case.  In Pakistan a new strain of cVDPV2 arose in the Quetta area, with one instance of paralysis.<ref>{{cite |title=Semi-Annual Status Report: July to December 2016|url=http://polioeradication.org/wp-content/uploads/2017/04/Status-Report_Jul-Dec2016.pdf|publisher=[[Organization:Global Polio Eradication Initiative|Global Polio Eradication Initiative]] |page=8|access-date=April 28, 2017}}</ref><ref>{{cite web|url=http://www.who.int/csr/don/27-december-2016-polio-pakistan/en/|title=Summary of poliovirus circulation in 2016 – Pakistan|publisher=WHO|date=27 December 2016}}</ref>

Environmental samples from [[Place:Hyderabad|Hyderabad]], India from January 2015 to May 2016 showed the ongoing presence of a cVDPV2 strain in that city, without diagnosed cases.<ref>{{cite news|author=Kaushik Swaminathan|title=Polio Strain Found in Hyderabad, India, Prompts Vaccination Drive|url=https://www.nytimes.com/2016/06/16/world/asia/india-polio-hyderabad-telangana.html?_r=0|date=15 June 2016|newspaper=New York Times|access-date=17 June 2016}}</ref> Due to shortages in the global supply of injectable vaccine, an emergency campaign was launched using vaccine at one fifth the normal dose (fractional-Dose Inactivated Polio Vaccine, or fIPV), the first mass vaccination using this dosage of injectable vaccine.<ref name="Bahl" />

Attacks on polio vaccination campaigns continued. A suicide bombing in Quetta in January and a pair of attacks by gunmen in Karachi in April targeted Pakistani security personnel protecting vaccinators,<ref>{{cite news|title=Bomb near Pakistan polio centre 'kills 15'|url=https://www.bbc.com/news/world-asia-35299597|date=13 January 2016|newspaper=BBC|access-date=21 January 2016}}</ref><ref>{{cite news|title=Police Officers Guarding Polio Workers Killed in Karachi, Pakistan|url=http://www.nbcnews.com/news/world/police-officers-guarding-polio-workers-killed-karachi-pakistan-n559041|date=20 April 2016|newspaper=NBC|access-date=20 January 2016}}</ref> while in January three Afghan vaccination workers disappeared and their bodies were found weeks later.<ref>{{cite news|title=Three Polio Workers Killed In Eastern Afghanistan|url=http://www.rferl.org/content/polio-workers-killed-afghanistan/27537282.html|date=7 February 2016|newspaper=Radio Free Europe|access-date=20 April 2016}}</ref>

Because cVDPV2 strains continued to arise from trivalent oral vaccine that included attenuated WPV2, in April and May 2016 this vaccine was replaced with a bivalent version lacking WPV2 as well as trivalent injected inactivated vaccine that cannot lead to cVDPV cases. This is expected to prevent new strains of cVDPV2 from arising and allow eventual cessation of WPV2 vaccination.<ref>{{Cite web|url=http://www.polioeradication.org/mediaroom/newsstories/Global-synchronisation-and-the-switch/tabid/526/news/1366/Default.aspx|title=Global synchronisation and the switch|last=|first=|date=|website=www.polioeradication.org|archive-url=https://web.archive.org/web/20160515042223/http://www.polioeradication.org/mediaroom/newsstories/Global-synchronisation-and-the-switch/tabid/526/news/1366/Default.aspx|archive-date=15 May 2016|dead-url=yes|accessdate=14 April 2016|df=dmy-all}}</ref>

{{clear}}

=== 2017 ===

{| class="wikitable" style="float:right; font-size:85%; margin-left:15px"
| colspan=5 |<div style="text-align: center;">'''Reported polio cases in 2017'''<ref name="WHO2014">{{cite web|url = http://apps.who.int/immunization_monitoring/en/diseases/poliomyelitis/case_count.cfm|title = Polio Case Count|date = 27 December 2017|accessdate = 27 December 2017|publisher = World Health Organisation}}</ref>
[[File:Polio worldwide 2017.svg|thumb|center]]
</div>
|-
! Country !! Wild<br />cases !! Circulating<br />vaccine-<br />derived<br />cases !! Transmission<br />status !! Type(s)
|-
|{{flag|Afghanistan}}
|14
|0
|{{color|#f00|endemic}}
|{{color|#f00|WPV1}}
|-
|{{flag|Pakistan}}
|8
|0
|{{color|#f00|endemic}}
|{{color|#f00|WPV1}}
|-
|{{flag|Democratic Republic of the Congo|name=DRC}}
|0
|22
|{{color|#00f|cVDPV only}}
|{{color|#00f|cVDPV2}}
|-
|{{Flag|Syria}}
|0
|74
|{{color|#00f|cVDPV only}}
|{{color|#00f|cVDPV2}}
|-
| '''Total''' ||22||96|| ||
|}
There were 22 reported WPV1 polio cases with onset of paralysis in 2017, down from 37 in 2016. Eight of the cases were in Pakistan and 14 in Afghanistan,<ref name=":6">{{Cite web|url=http://polioeradication.org/polio-today/polio-now/wild-poliovirus-list/|title=GPEI-Wild poliovirus list|last=|first=|date=|website=polioeradication.org|language=en-GB|access-date=2018-02-23}}</ref> where genetic typing showed repeated introduction from Pakistan as well as local transmission.<ref>{{cite journal|last1=Martinez|first1=Maureen |last2=Shukla|first2=Hemant |last3=Nikulin |first3=Joanna |last4=Wadood |first4=Mufti Zubair |last5=Hadler |first5=Stephen |last6=Mbaeyi |first6=Chukwuma |last7=Tangermann |first7=Rudolph |last8=Jorba |first8=Jaume |last9=Ehrhardt |first9=Derek |title=Progress Toward Poliomyelitis Eradication — Afghanistan, January 2016–June 2017 |journal=Morbidity and Mortality Weekly Report (MMWR)|volume=66|pages=854–858|year=2017|doi=10.15585/mmwr.mm6632a5}}</ref>  In Pakistan, transmission of several genetic lineages of WPV1 seen in 2015 had been interrupted by September 2017, though at least two genetic clusters remain.  In spite of a significant drop in detected cases in Pakistan, there was an increase in the percentage of environmental samples that test positive for the polio virus, suggesting gaps in identification of infected individuals.<ref>{{cite journal|last1=Elhamidi|first1=Youness |last2=Mahamad|first2=Abdirahman |last3=Safdar |first3=Muhammad |last4=Al Tamimi |first4=Wasan |last5=Jorba |first5=Jaume |last6=Mbaeyi |first6=Chukwuma |last7=Hsu |first7=Christopher H |last8=Wadood |first8=Zubair |last9=Sharif |first9=Salmaan |last10=Ehrhardt |first10=Derek |title=Progress Toward Poliomyelitis Eradication — Pakistan, January 2016–September 2017 |journal=Morbidity and Mortality Weekly Report (MMWR)|volume=66|pages=1276–1280|year=2017|doi=10.15585/mmwr.mm6646a4}}</ref><ref>{{cite web| last=Roberts | first=Leslie | title=‘What the hell is going on?’ Polio cases are vanishing in Pakistan, yet the virus won't go away | publisher=Science | doi=10.1126/science.aas9789 | url=https://www.sciencemag.org/news/2018/01/what-hell-going-polio-cases-are-vanishing-pakistan-yet-virus-wont-go-away | date=11 January 2018 | access-date=19 January 2018 }}</ref> In the third country where polio remains endemic, Nigeria, there were no cases, though as few as 7% of infants were fully vaccinated in some districts.<ref name="gwp2013" /><ref>{{cite journal|title=Progress Toward Poliomyelitis Eradication — Nigeria, January–December 2017 |last=Bolu |first=Omotayo, et al. | journal=Morbidity and Mortality Weekly Report (MMWR) | volume=67 | pages=253–256 | url=https://www.cdc.gov/mmwr/volumes/67/wr/mm6708a5.htm?s_cid=mm6708a5_x}}</ref>  An April 2017 spill at a vaccine production facility in the Netherlands resulted in one asymptomatic infection.<ref>{{cite journal|last1=Duizer|first1=E. |last2=Ruijs |first2=W. L. |last3= van der Weijden |first3=C. P. |last4=Timen |first4=A. |title=Response to a wild poliovirus type 2 (WPV2)-shedding event following accidental exposure to WPV2, the Netherlands, April 2017|journal=Eurosurveillance|volume=22|issue=21|page=30542|year=2017|doi=10.2807/1560-7917.ES.2017.22.21.30542}}</ref>

Laos was declared free of cVDPV1 in March,<ref name=":2">{{cite press release|date= 6 March 2017|title= The poliovirus transmission in Lao People’s Democratic Republic has ceased|url= http://www.wpro.who.int/laos/mediacentre/releases/2017/20170307-polio-transmission-lao-ceased/en/|agency= WHO|access-date= 4 April 2017}}</ref><ref>{{cite web|title=End of Outbreak in Lao Peoples Democratic Republic|publisher=GPEI|date=29 May 2017|accessdate=29 May 2017|url=http://polioeradication.org/news-post/end-of-outbreak-in-lao-peoples-democratic-republic/}}</ref> but two distinct cVDPV2 outbreaks occurred in the Democratic Republic of the Congo. One in Maniema province resulted in two April polio cases, and a second in February in Haut-Lomami and neighboring Tanganyika provinces came from a virus circulating there for at least a year, and had caused 20 cases by year's end and continued into the next year.<ref>{{cite web|last=Herriman|first=Robert|title=Polio update: Two cVDPV2 outbreaks reported in Democratic Republic of the Congo|publisher=Outbreak News Today|url=http://outbreaknewstoday.com/polio-update-two-cvdpv2-outbreaks-reported-democratic-republic-congo-39590/|date=25 May 2017|accessdate=25 May 2017}}</ref><ref>{{cite journal|last1=Alleman | first1=Mary M | last2=Chitale | first2=Rohit | last3=Burns | first3=Cara C | last4=Iber | first4=Jane | last5=Dybdahl-Sissoko2 | first5=Naomi | last6=Chen | first6=Qi | last7=Van Koko | first7=Djo-Roy | last8=Ewetola | first8=Raimi | last9=Riziki | first9=Yogolelo | last10=Kavunga-Membo | first10=Hugo | last11=Dah | first11=Cheikh | last12=Andriamihantanirina | first12=Rija | title=Vaccine-Derived Poliovirus Outbreaks and Events — Three Provinces, Democratic Republic of the Congo, 2017 | journal=Morbidity and Mortality Weekly Report (MMWR) | year=2018 | volume=67 | pages=300–305 | doi=10.15585/mmwr.mm6710a4}}</ref><ref name=DRCWHO>{{cite web|title=Circulating vaccine-derived poliovirus type 2 – Democratic Republic of the Congo|publisher=World Health Organization|date=10 July 2018|accessdate=13 August 2018|url=http://www.who.int/csr/don/10-july-2018-polio-drc/en/}}</ref>  In Syria a large outbreak began at Mayadin, [[Place:Deir ez-Zor Governorate|Deir ez-Zor Governorate]], a center of fighting in the Syrian Civil War and also spreading to neighboring districts saw 74 confirmed cases from a viral strain that had circulated undetected for about two years.<ref name=Branswell-Syria>{{cite news|last=Branswell|first=Helen|title=Polio outbreak is reported in Syria, WHO says|publisher=STAT|date=8 June 2017|accessdate=8 June 2017|url=https://www.statnews.com/2017/06/08/polio-outbreak-syria-who/}}</ref><ref>{{cite news|title=WHO says child from Raqqa among 15 new polio cases in Syria|publisher={{wipe|Reuters}}|url=https://www.reuters.com/article/us-mideast-crisis-syria-polio-idUSKBN19B1V8|date=20 June 2017|accessdate=20 June 2017}}</ref>  Circulation of multiple genetic lines of cVDPV2 was also detected in Banadir province, Somalia, but no infected individuals were identified.<ref name="WHO Somalia">{{cite web|title=Circulating vaccine-derived poliovirus type 2 – Somalia|date=9 March 2018|publisher=WHO|access-date=21 October 2018|url=http://www.who.int/csr/don/09-March-2018-polio-Somalia/en/}}</ref>  WHO's Strategic Advisory Group of Experts on Immunization recommended that cVDPV2 suppression be prioritized over targeting WPV1,<ref name="SAGEApr2017">{{Cite web|url=http://www.who.int/immunization/sage/meetings/2017/april/SAGE_April_2017_Meeting_Web_summary.pdf?ua=1|title=Summary of the April 2017 meeting of the Strategic Advisory Group of Experts on Immunization|last=|first=|date=|website=World Health Organization|language=en-GB|access-date=2017-05-15}}</ref> and according to protocol OPV2 is restricted to this purpose.

The 2016 global switch in vaccination methods resulted in shortages of the injectable vaccine,<ref>{{cite news|title=As hopes for polio eradication rise, the endgame gets complicated, and a vaccine runs short|last=Branswell|first=Helen|publisher=STAT|url=https://www.statnews.com/2017/05/19/polio-vaccine-shortages/|date=19 May 2017|accessdate=19 May 2017}}</ref> and led the WHO in April 2017 to recommend general use of the fIPV vaccination protocol, involving [[Medicine:Subcutaneous injection|subcutaneous injection]] of a lower dose than used in the standard [[Biology:Intramuscular injection|intramuscular]] delivery.<ref>{{cite news|title=WHO urges polio vaccine dose cut amid shortage|publisher=''The China Post''|location=Taipei|date=30 April 2017|access-date=12 May 2017|url=http://www.chinapost.com.tw/2017/04/30/496458/who-urges.htm}}</ref>

{{Clear}}

=== 2018 ===
{| class="wikitable" style="float:right; font-size:85%; margin-left:15px"
| colspan="5" |<div style="text-align: center;">'''Reported polio cases in 2018'<ref name="PolioThisWeek">{{cite web|url=http://polioeradication.org/polio-today/polio-now/this-week/|title=Polio This Week|publisher=Global Polio Eradication Initiative}}</ref>
[[File:Polio worldwide 2018.svg|thumb|center]]
</div>
|-
! Country !! Wild<br />cases !! Circulating<br />vaccine-<br />derived<br />cases !! Transmission<br />status !! Type
|-
|{{flag|Afghanistan}}
|16
|0
|{{color|#f00|endemic}}
|{{color|#f00|WPV1}}
|-
|{{flag|Pakistan}}
|4
|0
|{{color|#f00|endemic}}
|{{color|#f00|WPV1}}
|-
| {{flag|Papua New Guinea}} ||0||18||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV1}}
|-
| {{flag|Nigeria}} ||0||16||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}}
|-
|{{flag|Democratic Republic of the Congo|name=DRC}}
|0
|15
|{{color|#00f|cVDPV only}}
|{{color|#00f|cVDPV2}}
|-
| {{flag|Somalia}} ||0||13||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2<br />cVDPV3}}
|-
| {{flag|Niger}} ||0||6||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}}
|-
| '''Total''' ||20||68||||
|}
As of 16 October, there had been twenty reported WPV1 paralysis cases with an onset of paralysis in 2018 – sixteen in Afghanistan and four in Pakistan.<ref name="gwp2013">{{cite web|url=http://polioeradication.org/wp-content/uploads/2018/10/global-wild-poliovirus-2013-2018-20181016.pdf|title=Global Wild Poliovirus 2013 - 2018|last=|first=|date=|website=|archive-url=|archive-date=|dead-url=|accessdate=18 October 2018}}</ref><ref>{{Cite news|url=https://reliefweb.int/report/pakistan/eoc-kp-confirmed-first-polio-case-2018-kp|title=EOC KP confirmed first polio case of 2018 in KP|work=ReliefWeb|access-date=2018-09-08|language=en}}</ref>  In Pakistan, three of the cases occurred in a single district, Kohlu District in Balochistan, with the fourth in the north, in Charsadda District, Khyber Pakhtunkhwa,<ref name="PolioThisWeek" /> but viral circulation continues across much of the country, including several major urban areas, and it is detected in 14% of environmental samples.<ref>{{cite report|title=Pakistan Polio Update, August 2018|publisher=Government of Pakistan|access-date=18 October 2018|url=http://www.endpolio.com.pk/images/polio-briefer/Pakistan-Polio-Update-August-2018.pdf}}</ref>  Cases in Afghanistan represent two transmission clusters, one in Kandahar, Urozgan and Helmand Provinces in the south, the other in the adjacent Kunar and Nangarhar Provinces in the northeast, on the Pakistani border.<ref name="PolioThisWeek" /><ref>{{cite report|title=Polio Snapshot, Afghanistan, August 2018|publisher=UNICEF,WHO|date=30 August 2018 | access-date=18 October 2018 | url=http://applications.emro.who.int/docs/AFG/COPub_AFG_Aug_2018_20457_EN.pdf?ua=1}}</ref><ref name=Martinez>{{cite journal| last1=Martinez| first1=Maureen| last2=Shukla| first2=Hemant| last3=Ahmadi| first3=Meiland| last4=Inulin| first4=Joanna| last5=Widodo| first5=Mufti Sabari| last6=Ahmed| first6=Jamal| last7=Mbaeyi| first7=Chukwuma| last8=Jabra| first8=Jaime| last9=Gerhardt| first9=Derek| title=Progress Toward Poliomyelitis Eradication — Afghanistan, January 2017–May 2018 | journal=Morbidity and Mortality Weekly Report (MMWR)| volume=67| number=30| pages=833-837| year=2018| url=https://www.cdc.gov/mmwr/volumes/67/wr/mm6730a6.htm}}</ref> Roughly half of recent Afghanistan isolates were genetically closer to isolates from Pakistan than to other Afghani samples, suggesting significant trans-border transmission,<ref name="Martinez" /> with two separate common transmission corridors in the north and south, where different viral genetic subtypes are found.<ref name="Martinez" /><ref name="2017report">{{Cite web|url=http://polioeradication.org/wp-content/uploads/2017/12/polio-eradication-15th-IMB-Report-2017-11.pdf|title=Polio Eradication 15th Independent Monitoring Board Report|last=|first=|date=|website=|archive-url=|archive-date=|dead-url=|access-date=}}</ref><ref>{{Cite web|url=http://www.emro.who.int/images/stories/pakistan/Week_41_Oct_13_2018.pdf|title=Weekly AFP Surveillance update Pakistan Week 41|last=|first=|date=|website=|archive-url=|archive-date=|dead-url=|access-date=}}</ref>  In 2017, many of the detected viruses derived from long chains of undetected transmission,<ref name=2017report /> but long chain transmission may be subsiding in both Pakistan<ref>{{Cite news|url=http://www.who.int/news-room/detail/10-05-2018-statement-of-the-seventeenth-ihr-emergency-committee-regarding-the-international-spread-of-poliovirus|title=Statement of the Seventeenth IHR Emergency Committee  Regarding the International Spread of Poliovirus|work=World Health Organization|access-date=2018-09-14|language=en-US}}</ref> and Afghanistan<ref name="Martinez" /> in 2018.

Cases caused by vaccine-derived poliovirus have been reported in five countries.  In the Democratic Republic of Congo, at least one of the two 2017 outbreaks of cVDPV2 continued into 2018, with cases reported across several provinces. A new third distinct strain of cVDPV2 has been confirmed in Mongala Province, with the county's total from all strains at 15 cases.<ref name=DRCWHO /><ref name="PolioThisWeek" />  Two separate cVDPV2 outbreaks in Nigeria centered on Sokoto and Jigawa States have produced sixteen cases,<ref name="PolioThisWeek" /><ref>{{cite web|title=Circulating vaccine-derived poliovirus type 2 – Nigeria|publisher=World Health Organization|date=8 August 2018|accessdate=13 August 2018|url=http://www.who.int/csr/don/08-august-2018-polio-nigeria/en/}}</ref> with the latter outbreak also causing six cases in the neighboring Zinder Region, Niger. In Somalia, a strain of cVDPV2 first detected in [[Place:Mogadishu|Mogadishu]]'s Banadir Province in 2017 continues to circulate, and has spread as far as [[Place:Nairobi|Nairobi]], Kenya, and Gedo, Somalia, on the Ethiopian border.  It has caused several cases in Somalia, as has a newly-detected cVDPV3 strain found around the capitol, with thirteen total cases from the two strains, including one patient found to have been infected by both viruses.<ref name="WHO Somalia" /><ref name="PolioThisWeek" /><ref>{{cite report|title=Somalia cVDPV Outbreak Response Situation Report #3|publisher=WHO, UNICEF|date=20 August 2018|access-date=25 August 2018|url=http://www.emro.who.int/images/stories/Somalia_cVDPV_situation_report_Issue_3_21_August_2018.pdf?ua=1}}</ref>  In Papua New Guinea, a strain of cVDPV1 has arisen that has caused eighteen polio cases throughout the country.<ref name="PolioThisWeek" />  Response to the Syrian cVDPV2 outbreak continued into 2018, and virus transmission was successfully interrupted.<ref>{{cite journal| last1=Mbaeyi| first1=Chukwuma| last2=Wadood| first2=Zubair Mufti| last3=Moran| first3=Thomas Moran| last4=Ather| first4=Fazal| last5=Stehling-Ariza| first5=Tasha| last6=Nikulin| first6=Joanna| last7=Al Dafadi| first7=Mohammad| last8=Iber| first8=Jane| last9=Zomahoun| first9=Laurel| last10=Abourshaid| first10=Nidal| last11=Pang| first11=Hong| last12=Collins| first12=Nikki| last13=Asghar| first13=Humayun| last14=Butt| first14=Obaid ul Islam| last15=Burns| first15=Cara C.| last16=Ehrhardt| first16=Derek| last17=Sharaf| first17=Magdi| title=Strategic Response to an Outbreak of Circulating Vaccine-Derived Poliovirus Type 2 — Syria, 2017–2018| journal=Morbidity and Mortality Weekly Report (MMWR)| volume=67| number=24| pages=690–694| year=2018| url=https://www.cdc.gov/mmwr/volumes/67/wr/mm6724a5.htm}}</ref> {{Clear}}

== See also ==
* [[Biology:Eradication of infectious diseases|Eradication of infectious diseases]]
* [[Biology:Mathematical modelling of infectious disease|Mathematical modelling of infectious disease]]
* [[Social:Population health|Population health]]
* ''The Final Inch'', a documentary film about the eradication effort
* [[Medicine:Transmission risks and rates|Transmission risks and rates]]
* List of diseases eliminated from the United States

== Notes ==
{{Notelist}}

== References ==
{{Reflist|30em}}

== External links ==
* [http://www.polioeradication.org/ Global Polio Eradication]
* [http://crs.org/india/battling-polio-on-the-streets-of-india/ Brief Video: Battling Polio on India's Streets] Catholic Relief Services

[[Category:Vaccine controversies]]

{{Sourceattribution|Poliomyelitis eradication|1}}