VIENNA, AUSTRIA -- What if you could use a product--and not a condom--to prevent getting infected with HIV? That may feel like a fantasy, but it's actually edging closer to reality.

At the XVIII International AIDS Conference in Vienna, Austria, the exciting South African CAPRISA study showed that using a microbicide gel containing an anti-retroviral (ARV) drug before and after sex can prevent HIV in women at least 39 percent of the time. Many believe this good news is a major step in the notion of "treatment as prevention."

"[The CAPRISA study] folds into an even grander dream which is Pre-Exposure Prophylaxis (PrEP), an oral pill that an HIV-uninfected person takes to prevent infection," said Science magazine reporter Jon Cohen, author of that magazine's coverage of CAPRISA and Shots in the Dark: The Wayward Search for an AIDS Vaccine, in an interview on Tuesday. "It's a hugely promising approach because this says if [the microbicide] works, then [PrEP] has a high likelihood of working. And if PrEP works, then we have a whole new way to look at treatment as prevention."

Giving those who are not infected with a disease medicine to prevent it is not a new concept. This is how malaria is prevented. But around HIV specifically, the science hasn't yet proven that it's an effective or practical form of prevention--though the success of the microbicide research is raising expectations. Over the six-day conference in Vienna a number of panels discussed PrEP. Despite plenty of hope, no definitive answers emerged in response to the questions surrounding its use.

Since 2004 researchers have looked at PrEP as a way to stop the spread of HIV. Most PrEP strategies ask people to take medication, specifically tenofovir (prescribed as a pill under the brandname Viread) or tenofovir-emtricitabine (prescribed in pill form as Truvada), on an ongoing basis. These AIDS drugs are only taken once per day and have the fewest side effects. In fact, tenofovir was used in the CAPRISA study. PrEP shouldn’t be confused with PEP, Post-Exposure Prophylaxis, where someone who thinks they have been recently exposed to HIV takes ARVs after exposure to decrease their risk of acquiring the virus.

PrEP, if successful, would benefit all at-risk populations, but is especially promising for women, who bear the weight of the epidemic the world over. In the U.S. Black women are disproportionately infected, with only more gay and bisexual Black and White men becoming infected each year. PrEP, like microbicides, addresses an urgent need for a female-controlled HIV prevention method for women. Because of poverty, threat of violence, or cultural issues, women have few ways to protect themselves.

"Protection from transmission would not have to be negotiated with partners who are reluctant or unwilling to use a condom," says Mabel Bianco, M.D., about PrEP. She is the coordinator of the International AIDS Women's Caucus. "The choice would be in the hands of women. This has the potential to vastly impact the pandemic."

Currently scientists are conducting more than a dozen trials in high-risk populations around the world, including in Botswana, Brazil, Ecuador, Kenya, Malawi, Peru, South Africa, Tanzania, Thailand, Uganda, the United States and Zimbabwe. The U.S.-based Centers for Disease Control and Prevention (CDC) is sponsoring PrEP trials in Thailand in intravenous drug users, and in the United States with populations of gay and bisexual men.