Study finds new drug cut risk of infection by 39 percent.
For the first time, a gel has been shown to be effective in blocking HIV.
Researchers at the Centre for the AIDS Program of Research in Durban, South Africa found the vaginal gel cut the risk of infection by 39 percent.
889 women at high risk for HIV infection participated in the study.
Those who used the gel most frequently cut their risk by more than half.
The gel contains Tenofovir, a drug called that prevents hiv from growing inside human cells.
Scientists say this finding is "a game changer" because it gives women the opportunity to protect themselves from the disease.
It will likely be years before the gel is widely available.
Larger studies are still needed to confirm the results.
The study is published in the journal Science and was presented at the International AIDS Society meeting in Vienna.