Medicine:Number needed to vaccinate
Number needed to vaccinate (NNV) is a metric used in the evaluation of vaccines, and in the determination of vaccination policy. It is a specific application of the number needed to treat metric (NNT) that incorporates the implications of herd immunity.
NNV is the statistical inverse of incidence i.e. 1/incidence. In other words, in case of the vaccination for a disease with incidence of 1 per 1000, the NNV is 1000.
For example, one study reported a number needed to vaccinate of 5206 for invasive pneumococcal disease.
In order to determine a NNV, it is necessary to identify a specific population and a defined endpoint, because these can vary:
- Tuberculosis vaccination rates are much higher in Europe than in the United States.
- When evaluating a vaccine against chickenpox, it is necessary to define whether or not the endpoint would include shingles due to reactivation.
- If evaluating a HIV vaccine, the NNV may vary depending upon the expected standard of care in the absence of a vaccine, which may vary from continent to continent.
- If an infectious disease is acute and highly lethal, there may be large differences in the impact of the vaccine upon incidence and prevalence.
Despite the limitations, the NNV can serve as a useful resource. For example, it can be used to report the results of computer simulations of varying vaccination strategies.
- "The number needed to vaccinate (NNV) and population extensions of the NNV: comparison of influenza and pneumococcal vaccine programmes for people aged 65 years and over". Vaccine 22 (17–18): 2192–8. June 2004. doi:10.1016/j.vaccine.2003.11.052. PMID 15149776.
- Brisson M (2008). "Estimating the number needed to vaccinate to prevent herpes zoster-related disease, health care resource use and mortality". Can J Public Health 99 (5): 383–6. PMID 19009921.
- "Childhood influenza: number needed to vaccinate to prevent 1 hospitalization or outpatient visit". Pediatrics 120 (3): 467–72. September 2007. doi:10.1542/peds.2007-0167. PMID 17766517. http://pediatrics.aappublications.org/cgi/pmidlookup?view=long&pmid=17766517.
- "The impact and effectiveness of pneumococcal vaccination in Scotland for those aged 65 and over during winter 2003/2004". BMC Infect. Dis. 8: 53. 2008. doi:10.1186/1471-2334-8-53. PMID 18433473.
- "Adolescent and adult pertussis vaccination: computer simulations of five new strategies". Vaccine 22 (23–24): 3154–65. August 2004. doi:10.1016/j.vaccine.2004.01.067. PMID 15297068.
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