CONDITIONS OF VALIDATION AND USE OF THE SCREENING METHOD FOR VACCINE EFFICACY EVALUATION

If PV is the proportion of the target population vaccinated and PCV th e proportion of cases in the same population who have been previously vaccinated, vaccine efficacy can be computed as (PV-PCV)/[PV(1-PCV)]. In the screening method, this formula is currently applied to sample v alues. The objective of this paper is to provide the corresponding sta tistical tools. Taylor series expansion has been used to derive the bi as, variance and confidence interval of the estimate. The bias may be very high when vaccine efficacies are low. It is below 1% for vaccine efficacies higher than 80%. Monte Carlo simulations were used to asses s the departure from normality of the estimate. The number of subjects required by the method for given precisions are presented.