Daily HIV pill use yields strong results; Can reduce risk of getting virus by 73%

Researchers cautioned, however, that Truvada, an anti-retroviral drug now used by people already infected with HIV, achieves such stunning success only when taken diligently and used in combination with other prevention strategies.

Nevertheless, such eye-popping results, published Tuesday in the New England Journal of Medicine, produced applause from gay-rights and AIDS-activist groups and from the White House.

"I am encouraged by this announcement of groundbreaking research on HIV prevention," President Obama said after the NIH study findings were announced. "While more work is needed, these kinds of studies could mark the beginning of a new era in HIV prevention."

"These results represent a major advance in HIV prevention research," said Dr. Kevin Fenton, director of the Centers for Disease Control and Prevention's (CDC) National Center for HIV/AIDS, Viral Hepatitis, STD and TB Prevention.

"For the first time, we have evidence that a daily pill used to treat HIV is partially effective for preventing HIV among gay and bisexual men at high risk for infection, when combined with other prevention strategies," Dr. Fenton said. This is "exciting and welcome news."