Researchers have developed a vaginal gel that protects monkeys against HIV infection when applied up to three hours after sex. It may also be effective in humans.

In the search for a way to protect humans from HIV infection, researchers have discovered a vaginal gel that reduces the rate of HIV transmission among monkeys, when applied up to three hours after sex. Researchers believe that the gel could be effective for humans too. If so, it could be particularly helpful for women who have been sexually assaulted by someone who may be HIV positive.

The research, which was recently published in Science Translational Medicine, tested a new microbicidal, or microbe-killing, vaginal gel on macaque monkeys. The study did not show 100 percent protection. However, five out of the six monkeys were protected from infection.

The gel contains raltegravir, an antiretroviral drug that is already used to treat HIV. While some HIV-prevention gels are already available, they usually require a pre-exposure dose.

Researchers gave 12 monkeys vaginal washes of simian HIV to mimic sex with an infected monkey. Three hours later, six of these monkeys were treated with the newly developed gel, and the other six were given a placebo gel.

Of the six macaques given the new gel, only one became infected with HIV, while all six of the monkeys who were treated with the placebo fell ill.

In a separate part of the trial, only one of three monkeys given the microbicidal gel 30 minutes before exposure to the simian HIV became infected.

According to Walid Heneine, the study’s lead author and director of primate trials of HIV prevention methods for the Centers for Disease Control and Prevention (CDC), researchers were puzzled as to why two of the monkeys given the microbicidal gel still became infected.

Sharon L. Hillier, a professor of obstetrics at the University of Pittsburgh, told The New York Times that if the gel works in humans, it could be used for HIV prevention, much like Plan B or the morning-after pill for contraception.

Although success in monkey studies does not always translate into success in humans—and application of the research to humans may not occur in the immediate future—the results of this study are a boon for HIV-prevention research.

Commenting on the research findings, Dr. Kenneth Mayer, a visiting professor at Harvard Medical School and the medical research director at Boston’s Fenway Institute, told Healthline, “The findings are exciting since they are the first demonstration that post-coital gel use can be protective against HIV. The use of topical integrase inhibitors is also novel. The data are from an animal model, so we still have a long way to go before knowing whether the findings are translatable for humans. Nonetheless, the data suggest some additional ways to prevent HIV transmission, which is important.”

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