Number needed to vaccinate
Number needed to vaccinate (NNV) is a metric used in the evaluation of vaccines,[1][2][3] and in the determination of vaccination policy. It is defined as the average number of patients that must be vaccinated to prevent one case of disease. It is a specific application of the number needed to treat metric (NNT).
Derivation
[edit]NNV is the inverse of the absolute risk reduction of the vaccine. If the incidence in the vaccinated population is , and the incidence in the unvaccinated population is , then the NNV is .
For example, one study reported a number needed to vaccinate of 5206 for invasive pneumococcal disease.[4]
Significance
[edit]In order to determine a NNV, it is necessary to identify a specific population and a defined endpoint, because these can vary:[citation needed]
- 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.[5]
See also
[edit]References
[edit]- ^ Kelly H, Attia J, Andrews R, Heller RF (June 2004). "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): 2192–2198. 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): 383–386. doi:10.1007/BF03405246. PMC 6976184. PMID 19009921.
- ^ Lewis EN, Griffin MR, Szilagyi PG, Zhu Y, Edwards KM, Poehling KA (September 2007). "Childhood influenza: number needed to vaccinate to prevent 1 hospitalization or outpatient visit". Pediatrics. 120 (3): 467–472. doi:10.1542/peds.2007-0167. PMID 17766517. S2CID 25894405.
- ^ Mooney JD, Weir A, McMenamin J, et al. (2008). "The impact and effectiveness of pneumococcal vaccination in Scotland for those aged 65 and over during winter 2003/2004". BMC Infect. Dis. 8: 53. doi:10.1186/1471-2334-8-53. PMC 2386805. PMID 18433473.
- ^ Van Rie A, Hethcote HW (August 2004). "Adolescent and adult pertussis vaccination: computer simulations of five new strategies". Vaccine. 22 (23–24): 3154–65. doi:10.1016/j.vaccine.2004.01.067. PMID 15297068.