Epidemiologic metric
Number needed to vaccinate (NNV) is a metric used in the evaluation of vaccines, 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.
NNV is the inverse of the absolute risk reduction of the vaccine. If the incidence in the vaccinated population is formula_1, and the incidence in the unvaccinated population is formula_2, then the NNV is formula_3.
For example, one study reported a number needed to vaccinate of 5206 for invasive pneumococcal disease.
Significance.
In order to determine a NNV, it is necessary to identify a specific population and a defined endpoint, because these can vary:
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.
References.
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