Report No. 03-02
Date: April 3, 2003
Title: Estimating Vaccine Efficacy from Household Data Observed over Time
Author(s): Xiahong M. Davis and Michael J. Haber
Abstract
Estimation of vaccine efficacy has traditionally focused on the reduction in susceptibility to infection, or vaccine
efficacy for susceptibility (VES). A vaccine may also lower the infectiousness of a vaccinated person who became
infected. The relative reduction in infectiousness due to a vaccine is vaccine efficacy for infectiousness or VEI.
Estimation of VEI is challenging because it requires information on exposure to infection and gathering this type of
information is often expensive and difficult or even impossible. The problem of estimating VES and VEI is further
complicated by the fact that reliable infection outcome is often expensive or difficult to collect across the population
under study. Often, a closely related outcome may be used as a surrogate for the infection outcome. In this paper, a
semiparametric method that uses surrogate outcome and a validation sample is proposed for household data to
estimate VES and VEI. The proposed method shows improved efficiency as compared to using the validation sample
only and smaller bias as compared to using surrogate outcome only in estimating VES. Using household data is
shown to greatly improve the attenuation in VE S as compared to findings from previous studies. In estimating VEI,
the proposed method performs better when the true VE I is smaller.