New PrEP Efficacy Data Released Today

Just days before the International AIDS Society’s (IAS’s) 6th Conference on HIV Pathogenesis, Treatment and Prevention gets underway in Rome, new results were released from two trials showing that oral pre-exposure prophylaxis (PrEP)—the administration of antiretrovirals (ARVs) in an effort to prevent HIV infection—is an effective way to reduce the risk of HIV infection among heterosexual men and women.

Earlier this year, researchers reported results form a study known as iPrEx indicating that daily administration of ARVs was 44% effective in protecting men and transgendered women who have sex with men from HIV. Now, two more studies have extended those results to heterosexual men and women.

Results from one study, referred to as the Partners PrEP study, which enrolled 4,758 heterosexual serodiscordant couples in Kenya and Uganda, indicate that a daily dose of the ARV tenofovir reduced the risk of HIV infection by 62%, while daily dosing of the ARV Truvada (the combination of tenofovir and FTC) performed even better, reducing HIV infection risk by as much as 73%. Both ARV regimens were effective in preventing infection in men and women. These results were so favorable, the trial’s data safety monitoring board suggested releasing the results and discontinuing the placebo arm of the trial 18 months before the trial’s scheduled end date. The study, led by researchers at the University of Washington, is the largest PrEP study conducted thus far.

Investigators also reported other encouraging news: more than 97% of the daily doses were taken correctly in the Partners PrEP study, and 95% of those who were enrolled remained in the trial. There were also no significant safety events noted in the trial.

The other trial results released today came from the TDF2 study, a trial in Botswana that enrolled 1,219 sexually active men and women and was led by BOTUSA, a partnership of the US Centers for Disease Control and Prevention (CDC) and the government of Botswana. Investigators reported that in this trial, daily administration of Truvada reduced the risk of HIV infection in both men and women by approximately 63%. TDF2 was originally planned as a Phase III efficacy trial but was scaled back to an expanded safety trial after the HIV incidence in Botswana dropped and investigators concluded they would need to double enrollment to meet the pre-specified endpoint of 57 new infections among volunteers.

However, the TDF2 study did yield statistically significant results. Only nine infections occurred among the 601 participants who received Truvada, while 24 infections occurred among the 599 individuals who received placebo. Lynn Paxton, a CDC epidemiologist who helped coordinate the TDF2 study, noted that the overall HIV incidence in the placebo arm of the Partners PrEP study was about 1.9%, compared to 3% in the placebo arm of the TDF2 study. Paxton suggests that PrEP is so effective, not as many endpoints were needed to show efficacy.

Complete results of both the Partners PrEP and TDF2 studies will be presented at the IAS conference in Rome, which opens July 17.

As data showing PrEP is an effective HIV prevention strategy accumulates, advocates are suggesting this approach should be put into practice. The New York-based advocacy group AVAC, which advocates for vaccines, PrEP, and other HIV prevention options, is urging the World Health Organization to move quickly to develop guidelines for populations for whom PrEP has now been shown to be effective. One of the biggest challenges may be finding resources to implement PrEP in resource-constrained countries bearing the biggest burden of HIV/AIDS, where millions of HIV-infected people go without these life-saving ARVs for treatment.

Meanwhile, in the wake of the most recent PrEP results, the CDC says it will be reviewing data from all of the trials involving heterosexual men and women and will begin working to develop guidance on the use of PrEP among heterosexual men and women in the United States.