As I mentioned in my speech to the XVIII International AIDS Conference on Monday, one promising area in the fight against HIV/AIDS is antiretroviral (ARV)-based prevention: pills, injections, and gels that contain the drugs now used for treatment.

And so it really was a privilege to be in Vienna when the incredibly exciting results of a new study were released. The Centre for the AIDS Programme of Research in Africa (CAPRISA) microbicide trial, the first of a new generation of ARV-based microbicides, showed reduced risk of HIV and herpes infections in women. This is the first time that a microbicide has been found to be effective.

What makes this so important is that we are a big step further in putting HIV prevention in the hands of women, who account for the majority of HIV infections worldwide.

The CAPRISA microbicide is a topical gel that contains tenofovir—an antiretroviral drug widely used to treat HIV infections—that women in the study inserted up to 12 hours before sex and soon after having sex for a maximum of two doses in 24 hours.

The tenofovir gel was found to be 39 percent effective in reducing a woman's risk of becoming infected with HIV during sex. The study also found that the microbicide is 51 percent effective in preventing genital herpes, which is important because women with genital herpes are at greater risk for HIV infection. Widespread use of the gel, at this level of protection, could prevent more than half a million new HIV infections in South Africa alone over the next ten years, saving many lives.

The CAPRISA microbicide trial findings are an exciting advance for HIV prevention. They give us reason to be hopeful, not just for an effective microbicide, but also for other ARV-based prevention tools now in development. As with any promising new HIV prevention tool, we look forward to discussions on how we might collaborate with other funders to support projects to confirm and extend these findings.

I’m really glad I attended the conference this year. As I said in my speech, even as we advocate for more funding, we need to be much more efficient in our approaches for treatment and prevention. But there was tremendous energy in Vienna, and I am optimistic that we can push ourselves to make the most of every dollar of funding, to identify the most effective ways to save lives, and to share what we learn as widely as possible.

This blog post was originally posted on The Gates Notes.