Back HIV Prevention Pre-exposure (PrEP) IAS 2011: New Studies Add Evidence that PrEP Reduces HIV Infection Risk

IAS 2011: New Studies Add Evidence that PrEP Reduces HIV Infection Risk

Pre-exposure prophylaxis (PrEP) using tenofovir/emtricitabine (the drugs in Truvada) lowers the risk of HIV transmission among heterosexuals, according to 2 African studies to be presented next week at the 6th International AIDS Society Conference of HIV Pathogenesis, Treatment and Prevention (IAS 2011).

The latest findings from the Partners PrEP and TDF2 trials mirror earlier results for gay and bisexual men in the iPrEx trial. However, another recent study -- FEM-PrEP -- was unable to demonstrate a protective effect for heterosexual women in Africa.

The Partners PrEP trial enrolled nearly 5000 participants at 9 sites in Kenya and Uganda. Preliminary data announced today by the University of Washington showed that daily oral tenofovir/emtricitabine reduced the rate of HIV transmission among serodiscordant heterosexual couples.

  • 18 new infections occurred among participants assigned to tenofovir alone, 13 among people taking tenofovir/emtricitabine, and 47 among those in the placebo arm.
  • Tenofovir alone reduced infection risk by 62%, while the tenofovir/emtricitabine combination did so by 73%.

“This is an extremely exciting finding for the field of HIV prevention. Now, more than ever, the priority for HIV prevention research must be on how to deliver successful prevention strategies, like PrEP, to populations in greatest need,” said study co-chair Jared Baeten.

“This study demonstrates that antiretrovirals are a highly potent and fundamental cornerstone for HIV prevention and should become an integral part of global efforts for HIV prevention,” added principal investigator Connie Celum.

The TDF2 trial, sponsored by the U.S. Centers for Disease Control and Prevention (CDC) and conducted in partnership with the Botswana Ministry of Health, found that once-daily oral tenofovir/emtricitabine reduced the risk of acquiring HIV by about two-thirds overall in a study population of heterosexual men and women.

  • 9 out of 601 participants who received tenofovir/emtricitabine were newly infected during the study, compared with 24 out of 599 placebo recipients.
  • Overall, PrEP lowered infection risk by 63%, a statistically significant reduction.
  • Looking only at infections occurring while participants were using the drugs, the protective effect increased to 78%.

“These are exciting results for global HIV prevention," said Kevin Fenton, director of CDC’s National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention. "We now have findings from two studies showing that PrEP can work for heterosexuals, the population hardest hit by HIV worldwide...Taken together, these studies provide strong evidence of the power of this prevention strategy.”

The CDC's announcement of the findings urged heterosexual men and women and their healthcare providers in the U.S. to wait for forthcoming guidance before considering PrEP. However, but if PrEP is deemed urgent, they can follow previously published procedures for PrEP use for men who have sex with men (available at 

"PrEP presents a unique HIV prevention advantage because it can help stop the cycle of infections from people who are newly infected with HIV but unaware of their status," said iPrEx trial chair Robert Grant in response to the news. "Making PrEP available is also an important strategy to draw people in to HIV testing and help HIV-negative people remain negative."

Comparing outcomes from Partners PrEP, TDF2, iPrEx, and FEM-PrEP, it is not clear why trials using the same biomedical prevention strategy have yielded conflicting results.

Possible explanations for the unexpected high infection rate in FEM-PrEP include low adherence, sharing of medications between the participants in the Truvada and placebo groups, biological factors, chance, or a combination of factors, according to a press release from Family Health International, which conducted FEM-PrEP.

All these trials -- and their real-life implications -- will be a major topic of discussion at IAS 2011. Results from Partners PrEP and TDF2 will be presented on Wednesday, July 20, 2011. IAS 2011 will also feature a satellite session on “What Does the Future of ARV-based Prevention Look Like” (Monday, 18 July, 18:30) and a cross-track bridging session on “Use of Antivirals in Prevention: Current Challenges and Controversies” (Tuesday, 19 July, 16:30).



Pivotal Study Finds that HIV Medications are Highly Effective as Prophylaxis against HI V Infection in Men and Women in Africa. University of Washington. Press release. July 13, 2011.

Centers for Disease Control and Prevention. CDC Trial and Another Major Study Find PrEP Can Reduce Risk of HIV Infection among Heterosexuals. Press release. July 13, 2011.

Family Health International. Partners PrEP and TDF2 pre-exposure prophylaxis trials both demonstrate effectiveness in preventing HIV infection among heterosexuals. Press release. July 13, 2011.

Two Major Studies Prove HIV Pre-Exposure Prophylaxis (PrEP) Works in in Heterosexual Women and Men. Press release. July 13, 2011.

International AIDS Society. IAS 2011 organizers congratulate researchers on new data showing PrEP can reduce risk of HIV infection among heterosexuals. Press release. July 13, 2011.