Sensitivity, specificity, and vaccine efficacy.

We study the effects of imperfect sensitivity and specificity on estimation of vaccine efficacy (VE). We show that a specificity of <1.0 (i.e., some noncases are classified as cases) can reduce the value of the estimate of VE. One may attempt to adjust the estimate by accounting for the values of sensitivity and specificity. This increases the variance of the estimate of VE and leads to larger sample size requirements. Alternatively, one may adopt the diagnosis method as the disease definition.