TIME Magazine's Top 10 Medical Breakthroughs of 2011

#3. HIV Treatment As Prevention

The treatment of HIV has come a long way, thanks to antiretroviral (ARV) drugs that can lower levels of the virus in the body, keeping people healthy and reducing the risk of HIV transmission. Increasingly, though, studies have also shown that the same drugs used to treat existing infections can also help protect HIV-free people from becoming infected.

This year, two groundbreaking trials — the first to involve heterosexual men and women — showed that HIV-free people were significantly less likely to become infected with the virus if they took the antiretroviral drug Truvada (a combination pill that contains the drugs tenofovir and emtricitabine) every day.

In one study led by University of Washington researchers, which involved 4,758 heterosexual couples in which one partner was HIV positive and the other was not, transmission of the virus was reduced by 73% after three years, compared with placebo, when the uninfected partner took the antiretroviral pill. In another study of 1,200 healthy, sexually active men and women, led by the Centers for Disease Control and Prevention, taking Truvada reduced the risk of HIV infection by 63%.

The results add to the evidence that using ARVs could help control the still growing AIDS epidemic in the developing world, where most new infections occur in heterosexual couples. Public health officials face significant obstacles in making ARVs widely available in these regions, but if they can, they might finally be able to curb the epidemic.

(taken from the TIME Specials section of Time.com)