A trial that had originally been planned to run until 2015, testing whether treating an HIV-infected person with antiretroviral drugs could prevent that person from passing the disease along to his partner, stopped today. Because it was so successful.

The trial, sponsored by the U.S. National Institute of Allergy and Infectious Diseases, was called off after a data review panel found that early treatment benefits were already apparent. According to Nature:

Among 866 couples assigned to the early treatment group, only one new infection occurred, in contrast to 27 new infections among the 877 couples in which the HIV-infected partner waited to start treatment.

"The findings of this study strongly indicate that treating an HIV-infected individual with antiretroviral drugs sooner rather than later can have a major impact on reducing the risk of HIV transmission to his or her sexual partner," [NIAID director Anthony] Fauci said.

While the news is heartening, it's far from a silver bullet against HIV; UNAIDS estimates that over 16 million people living with the virus don't know they're infected, and aggressive antiretroviral treatment is a painfully expensive proposition.

But! It's a piece of the puzzle. The findings of the study, combined with increased awareness and the use of other prevention methods (read: condoms), could some day go a long way towards beating back HIV, if not banishing it outright. [Nature]