American Journal of Epidemiology Vol. 136, No. 3: 328-343
Copyright © 1992 by The Johns Hopkins University School of Hygiene and Public Health
research-article |
Interpretation and Estimation of Vaccine Efficacy under Heterogeneity
Division of Biostatistics, Emory University School of Public Health Atlanta, GA.
Reprint requests to Dr. M. Elizabeth Halloran, Division of Biostatistics, Emory University School of Public Health, 1599 Clifton Road NE, Atlanta, GA 30329.
Interpretation and estimation of vaccine efficacy is complicated when the vaccine effect is heterogeneous across vaccinated strata. If a person has a certain susceptibility, or probability of becoming infected conditional on a specified exposure to infection, then one effect of a vaccine would be to reduce that susceptibility, possibly to zero. Vaccine efficacy is a function of the relative susceptibilities in the vaccinated and unvaccinated persons. Under heterogeneity of vaccine effect, a general expression for a summary vaccine efficacy parameter is a function of the vaccine efficacy in the different vaccinated strata weighted by the fraction of the vaccinated subpopulations in each stratum. Interpretation and estimability of the summary vaccine efficacy parameter depends on whether the strata are identifiable, and whether the heterogeneity is host-or vaccine-related. Bounds are derived for the summary vaccine efficacy when the strata are not identifiable for the case of an outbreak of an acute infectious disease. The upper bound assumes that everyone is equally affected by the vaccine, and the lower bound assumes that some are completely protected while others have no protection. The biologic interpretation of the two bounds is different. Am J Epidemiol 1992; 136: 32843
epidemiologic methods; immunization; infectious diseases; vaccination; vaccines
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