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:

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.

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