A Trial of an Anti-HIV Gel in Women Is Halted

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To contain the AIDS epidemic, it will take far more than simply finding and treating every patient who is infected with HIV. To truly halt the virus’ march, you will also need to shield healthy people from being infected in the first place.

That was the idea behind Voice (for Vaginal and Oral Interventions to Control the Epidemic), a trial of two anti-HIV pills and a microbicide gel to protect women from infection with HIV during sex. But on Friday, scientists stopped the gel portion of the trial, which involved about 2,000 high-risk women, because there was no difference in infection rates between women getting the anti-HIV vaginal gel and those getting a placebo.

The gel was designed to kill HIV in the vagina, before it had an opportunity to infect cells. It’s not clear why the gel failed in the current trial, particularly given that it appeared effective in a preliminary study reported last year. In that study of 889 women in South Africa, the gel, which contains 1% of the anti-HIV drug tenofovir in an antimicrobial solution, reduced infection by 39% over 2½ years compared with a placebo; in women who used the gel most faithfully before and after intercourse, it cut HIV infection risk by 54%.

“We don’t know precisely why it didn’t work,” says Dr. Anthony Fauci, director of the National Institutes of Health’s National Institute of Allergy and Infectious Diseases, which funded the current trial study. “But my strong suspicion is that women who had to put the gel in every day probably got tired of it.”

Compliance is an important factor when it comes to a strategy for preventing HIV in healthy people, says Fauci, since no preventive method can work if it’s not used. That’s why the most powerful ways to halt any disease, including AIDS, involve one-time treatments that have lasting effects, such as vaccines. But developing an immunization against the wily AIDS virus is proving more challenging than researchers had anticipated. So researchers have been testing other preventive measures, such intensive counseling about safe sex practices, including reducing the number of partners and using condoms, but so far none have shown much promise in stemming the tide of new HIV infections.

The microbicidal gel had looked promising, since it was designed to attack HIV almost as soon as it entered the body, rather than merely creating a barrier between the virus and healthy cells like some previous failed gels. Evidence suggests that the sooner HIV is dispatched, either by the immune system or by powerful anti-HIV drugs, the less likely the virus is to cause infection and lead to full-fledged AIDS.

The vaginal gel had the added advantage of putting the power of prevention in the hands of women, who are disproportionately affected by HIV in much of the developing world, and are in desperate need of a way to protect themselves — often secretly — during sexual encounters. But the gel has to be applied every day, and compliance with any daily activity can be challenging.

The results are the second blow to the Voice trial. The two other arms of the trial involve women taking tenofovir in pill form or another anti-HIV pill called Truvada (a combination of tenofovir and emtricitabine); in both arms, the drugs were compared to placebos. In September, the study leaders stopped the tenofovir portion of the study, since there was no significant difference in rates of HIV infection between women taking the drug and those taking placebo. The researchers will continue to test the effectiveness of Truvada in protecting healthy women from HIV infection. Those results, along with a more thorough analysis of the vaginal gel and tenofovir arms, are expected by 2013.

Alice Park is a writer at TIME. Find her on Twitter at @aliceparkny. You can also continue the discussion on TIME’s Facebook page and on Twitter at @TIME.

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