HIV control through treatment durably prevents heterosexual transmission of virus

In 2011, the HPTN 052 study investigators reported a breakthrough: Starting HIV treatment early, when the immune system is relatively healthy, reduced the risk of sexually transmitting the virus to an uninfected partner by 96 percent over 18 months. Based on additional data gathered since 2011, today's finding unequivocally demonstrates the enduring power of HIV-controlling antiretroviral therapy to greatly reduce sexual transmission of the virus.

"The study now makes crystal clear that when an HIV-infected person takes antiretroviral therapy that keeps the virus suppressed, the treatment is highly effective at preventing sexual transmission of HIV to an uninfected heterosexual partner," said NIAID Director Anthony S. Fauci, M.D. "For heterosexuals who can achieve and maintain viral suppression, the risk to their partners is exceedingly low."

The HPTN 052 trial was designed to evaluate whether antiretroviral therapy reduces sexual transmission of HIV. Beginning in April 2005, the study enrolled 1,763 heterosexual couples ages 18 or older in Botswana, Brazil, India, Kenya, Malawi, South Africa, Thailand, the United States and Zimbabwe. Each couple included one partner with HIV infection and one without. Infected participants were assigned at random either to start antiretroviral therapy right away, while their immune system was relatively healthy, or to delay starting treatment until their immune system weakened or they developed an AIDS-defining illness, consistent with World Health Organization guidelines at the time. All participants received condoms and counseling on how to protect their partners from sexual transmission of HIV.

Once the investigators reported their landmark data in 2011, all infected study participants were offered the opportunity to begin antiretroviral therapy right away, and the trial continued for another four years, concluding this spring. At the end of the study, 1,171 couples remained in the trial.

Investigators report today that starting antiretroviral therapy early reduced HIV transmission by 93 percent over the course of the study. Only eight cases of HIV transmission occurred in uninfected partners of HIV-infected participants who received antiretroviral therapy. Four of these infections were diagnosed shortly after the start of treatment. In these cases, the virus most likely was transmitted just before antiretroviral therapy began or right after it commenced, before treatment had fully suppressed HIV replication. The other four infections occurred in study participants for whom treatment no longer was working and the virus was replicating. Treatment failure may have occurred because HIV-infected participants did not take their antiretroviral drugs as prescribed or had an HIV strain that was resistant to one or more of the drugs in their treatment regimen.

The lack of sexual transmission of HIV by virally suppressed individuals in this large study provides robust evidence that antiretroviral therapy started at any time in the course of infection can prevent heterosexual HIV transmission if viral suppression is achieved and maintained, the investigators note.

"Throughout our decade-long study with more than 1,600 heterosexual couples, we did not observe HIV transmission when the HIV-infected partner's virus was stably suppressed by antiretroviral therapy," said Myron Cohen, M.D., the study's principal investigator. Dr. Cohen is Associate Vice Chancellor for Global Health at the University of North Carolina at Chapel Hill and director of the university's Institute for Global Health and Infectious Diseases. "These findings illustrate that treatment is an incredibly powerful tool for HIV prevention."

HPTN 052 investigators also are reporting findings today about relationships between viral load, viral suppression, treatment failure and drug resistance. The researchers found that having a relatively high level of HIV in the blood at the start of therapy was associated with a longer time to viral suppression, which, in turn, was associated with both the occurrence of treatment failure and a shorter time to treatment failure. Thus, having a relatively high viral load at the start of treatment could increase the risk for HIV transmission, the scientists suggest.

In addition, the investigators found that among the HPTN 052 participants who started antiretroviral therapy early but failed treatment before May 2011, those who had a higher viral load when they joined the study were likely to develop resistance to their antiretroviral drugs. Additional analysis is needed to clarify this association, according to the investigators.