Preliminary results from two large studies have now shown that a daily antiretroviral tablet taken by people who do not have HIV reduces their risk of contracting the virus by up to 73 percent.
The Partners PrEP trial involved 4758 HIV-discordant couples in Kenya and Uganda; the TDF2 trial involved 1219 men and women in Botswana.
The studies looked at both tenofovir or tenofovir plus emtricitabine (Truvada) and found that each, when taken in advance by the HIV-negative partner as a pre-exposure prophylaxis (PrEP), can prevent heterosexual transmission of HIV from men to women and from women to men. A previous study (iPrEx) had already shown PrEP reduced HIV transmission among men who have sex with men (MSM) last fall, but it was not previously known if the strategy would work in heterosexuals.
Next steps in the U.S. Centers for Disease Control and Prevention (CDC)-funded TDF2 study include offering Truvada to all HIV-uninfected trial participants for one year, and conducting a review of all relevant trial results with the aim of developing guidance about the use of PrEP to prevent HIV infection among heterosexual men and women in the United States.
The data safety monitoring board in the Partners PrEP trial stopped the trial 18 months early because of the clear benefit of PrEP, but supports continuation of the two drug arms of the trial to garner additional knowledge about the relative efficacy of tenofovir compared with tenofovir plus emtricitabine. Efficacy for tenofovir and emtricitabine/tenofovir were not statistically significant. But there are additional issues relevant to implementation with respect to the two drugs, including cost and the risk of drug resistance.
Sixty-two percent of HIV uninfected participants in the study were male; 38 percent were female. In both arms, PrEP medications reduced HIV risk in men and women. Notably, one-third of HIV uninfected study participants reported sexual activity outside the partnership during the study. When queried by a member of the audience about sexual activity outside the partnership by HIV-infected participants, Dr. Jared Baeten, a Partners PrEP principal investigator, indicated he did not have that information available. Dr. Baeten called for community-based PrEP demonstration projects based on the results of the two trials.
The Partners PrEP clinical trial was funded by the Bill & Melinda Gates Foundation.