The population level implications of imperfect HIV vaccines were studied using a mathematical model. A criterion for determining the utility of a vaccine at the population level is introduced, and 2 useful summary measures, namely, vaccine utility (ϕ) and vaccine infection fitness (ψ), are derived and shown to characterize the population-level utility once vaccine efficacies are determined. The utility of the vaccine alone does not guarantee a substantial impact, however, because the effectiveness of partially effective vaccines also depends on the prevailing level of HIV infectious spread. Therefore, a second criterion is introduced through a third summary measure, the hazard index (ξ), to describe the effectiveness of a vaccine in substantially reducing HIV incidence. The qualitative features of the impact are delineated by studying 4 distinct scenarios of HIV vaccination. Accordingly, our work delineates the link between vaccine efficacies and the impact of vaccination at the population level and provides the tools for vaccine developers to assess the utility and effectiveness of a given imperfect vaccine straightforwardly and rapidly.
From the *Statistical Center for HIV/AIDS Research and Prevention, Fred Hutchinson Cancer Research Center, Seattle, WA; †Center for Studies in Demography and Ecology, University of Washington, Seattle, WA; ‡Department of Infectious Diseases Epidemiology, Faculty of Medicine, Imperial College London, London, United Kingdom; and the §Program of Biostatistics and Biomathematics, Fred Hutchinson Cancer Research Center and Department of Biostatistics, School of Public Health and Community Medicine, University of Washington, Seattle, WA.
Received for publication September 8, 2006; accepted April 24, 2007.
Research supported by the University of Washington Center for AIDS Research, a National Institutes of Health-funded program (P30 AI 27757).
Reprints: Laith J. Abu-Raddad, PhD, Statistical Center for HIV/AIDS Research and Prevention, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue North, LE-400, PO Box 19024, Seattle, WA 98109 (e-mail: email@example.com).