HIV Drugs May Prevent Infection in Healthy Individuals

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As effective as the antiviral drugs have been in controlling the spread of HIV, the ultimate goal of any AIDS therapy is to prevent infection with the virus in the first place. And so far, nothing — from vaccines to gels — has proven up to the task of holding off HIV.

But in an exciting study published in the New England Journal of Medicine, researchers report that the very drugs that have helped to quell HIV in already infected patients may be effective in blocking infection in healthy, uninfected individuals as well. (More on Time.com: How Not to Get Sick)

In a trial involving nearly 2,500 HIV-negative gay men who were at high risk of contracting HIV, in six countries, scientists found that those who took the currently prescribed treatment dose of a combination anti-HIV medications known as Truvada had a 44% lower rate of HIV infection than those taking a placebo during the study’s longest follow up of nearly three years. Among those who took their medications more faithfully on a daily basis, the benefit was even greater; their risk of acquiring HIV dropped to 73% compared to placebo.

“These results represent a major advance in HIV prevention research,” said Dr. Kevin Fenton, director of the Centers for Disease Control (CDC) National Center for HIV-AIDS, Viral Hepatitis, STD and TB Prevention in a statement. “For the first time, we have evidence that a daily pill used to treat HIV is partially effective for preventing HIV among gay and bisexual men at high risk for infection.”

The excitement was echoed by others in the HIV community, who have been pushing for a stronger preventive strategy to combat the growing epidemic of cases, particularly in the developing world. “The study is really quite impressive, and the data are very robust, really strong,” says Dr. Anthony Fauci, director of the National Institutes of Health’s National Institute of Allergy and Infectious Diseases. The NIH, along with the Bill and Melinda Gates Foundation, funded the study, which took place at 11 different sites. (More on Time.com: Are HIV Rates in Gay Men Really ‘Out of Control’?)

Fauci is particularly encouraged by the data, since a closer look at the difference in HIV infection rates among those taking medications suggests that any exposure to the potent anti-HIV drugs can be effective in thwarting infection. For instance, among those in the drug arm, the volunteers who showed any measurable level of medication, no matter how faithfully they were popping their daily pills, had a 13-fold lower rate of HIV infection than those who showed no measurable level of drug in their system. “This is really huge; this is a very impressive result,” he says. “As with any new treatment strategy, it’s all about whether you adhere to the regimen.”

In fact, Fauci suspects that many physicians are already prescribing antiretroviral medications this way, in an attempt to head off infections in uninfected but high-risk individuals. These findings should bolster that practice, he believes, even as government health officials decide whether the results are robust enough to justify recommending anti-HIV drugs as a prevention strategy.

In the meantime, while the positive results suggest that antiretroviral drugs may be a critical part of a strong prevention program, experts note that the findings are not a license to abandon safe sex with condoms. The drugs do not alter the immune system in any way, nor does it prime the body the way that a vaccine would against HIV. These medications act only in the presence of HIV, to block its ability to infect and replicate in the body’s healthy cells, so the prevention strategy simply ensures that the drugs are in place, ready to act at the first encounter with the virus. The study participants were also all educated about risk-reduction practices, such as safe sex, and were provided with condoms and counseling as well as treatment for sexually transmitted diseases. (More on Time.com: Portugal’s Drug Experience: New Study Confirms Decriminalization Was a Success)

“[The] results are exciting, but it is not time for anyone to stop using condoms or stop following proven prevention methods,” said Fenton. “[The study] cannot be seen as the first line of defense against HIV.”

Fauci agrees, adding that more research will be needed to assess the effectiveness of the drugs in preventing infection among women, as well as heterosexual men. And because the drugs do have side effects, including potentially unhealthy changes in lipid levels, other studies will also investigate whether people could use the drugs intermittently as a prevention-based strategy — only, for example, when they plan on being sexually active.

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