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Predicting the Impact of a Partially Effective HIV Vaccine and Subsequent Risk Behavior Change on the Heterosexual HIV Epidemic in Low- and Middle-Income Countries: A South African Example

Andersson, Kyeen M MD, PhD*∥; Owens, Douglas K MD†‡; Vardas, Eftyhia MD§; Gray, Glenda E MD§; McIntyre, James A MD§; Paltiel, A David PhD*

JAIDS Journal of Acquired Immune Deficiency Syndromes: September 1st, 2007 - Volume 46 - Issue 1 - p 78-90
doi: 10.1097/QAI.0b013e31812506fd
Epidemiology and Social Science

We developed a mathematical model to simulate the impact of various partially effective preventive HIV vaccination scenarios in a population at high risk for heterosexually transmitted HIV. We considered an adult population defined by gender (male/female), disease stage (HIV-negative, HIV-positive, AIDS, and death), and vaccination status (unvaccinated/vaccinated) in Soweto, South Africa. Input data included initial HIV prevalence of 20% (women) and 12% (men), vaccination coverage of 75%, and exclusive male negotiation of condom use. We explored how changes in vaccine efficacy and postvaccination condom use would affect HIV prevalence and total HIV infections prevented over a 10-year period. In the base-case scenario, a 40% effective HIV vaccine would avert 61,000 infections and reduce future HIV prevalence from 20% to 13%. A 25% increase (or decrease) in condom use among vaccinated individuals would instead avert 75,000 (or only 46,000) infections and reduce the HIV prevalence to 12% (or only 15%). Furthermore, certain combinations of increased risk behavior and vaccines with <43% efficacy could worsen the epidemic. Even modestly effective HIV vaccines can confer enormous benefits in terms of HIV infections averted and decreased HIV prevalence. However, programs to reduce risk behavior may be important components of successful vaccination campaigns.

From the *Department of Epidemiology and Public Health, Yale University School of Medicine, New Haven, CT; †Veterans Affairs Palo Alto Health Care System, Palo Alto, CA; ‡Center for Primary Care and Outcomes Research/Center for Health Policy, Stanford University, Stanford, CA; and the §Perinatal HIV Research Unit, University of the Witwatersrand, Johannesburg, South Africa.

Received for publication February 1, 2007; accepted May 23, 2007.

∥Research undertaken as part of graduate studies in the MD/PhD program at Yale University and under the maiden name Kyeen Mesesan.

Supported by the National Institute on Drug Abuse (grant RO1DA015612) and the National Institute of General Medical Sciences Medical Scientist Training Program (grant GM07205).

Preliminary data from this study presented at the Society for Medical Decision Making Annual Meeting, Atlanta, GA, October 17-20, 2004; Annual National MD/PhD Student Conference, Keystone, CO, July 29-31, 2005; and Conference on Retroviruses and Opportunistic Infections, Denver, CO, February 5-8, 2006.

Reprints: Kyeen M. Andersson, MD, PhD, Department of Epidemiology and Public Health, Yale University School of Medicine, 60 College Street, New Haven, CT 06510 (e-mail:

© 2007 Lippincott Williams & Wilkins, Inc.