The Partners in Prevention HSV/HIV Transmission Study is the largest trial of its kind with over 3,400 HIV discordant couples (where one partner is HIV infected, the other HIV uninfected) from 14 sites in 7 countries in Eastern and Southern Africa (Uganda, Kenya, Rwanda, Tanzania, Zambia, Botswana and South Africa).

The Partners in Prevention study is a randomized, double-blinded, placebo-controlled study to determine whether the use of acyclovir by people who are infected with both HSV-2 and HIV can reduce the likelihood that they will transmit HIV to their HIV uninfected sexual partners. During the study, the HSV/HIV infected partner takes 400 milligram (mg) twice daily for up to 24 months. Researchers randomly assigned half of the study volunteers to a group that received 400 mg acyclovir tablets; the other half received placebo tablets. None of the study volunteers, clinical staff or researchers knew which specific group the volunteers were assigned.

Sites are implementing couples counseling and HIV testing and educating communities about HIV discordance. Participants are provided with condoms, regular exams, and extensive counseling to reduce their risk for HIV infection throughout the study. Participants who become infected with HIV during the study are referred for appropriate medical care and treatment in their community.