Early drug treatment for HIV can dramatically reduce the odds a person will pass the virus to an uninfected sexual partner.
The protective effect is so dramatic that an international study, begun in 2005, was halted before its scheduled end in 2015. Bottom line: Early treatment of the infected person with antiretroviral drugs cut the risk of HIV transmission to the uninfected partner by 96 percent.
This study, funded by the National Institute of Allergy and Infectious Disease, tested the approach by randomly assigning HIV-infected people to drug treatment immediately upon diagnosis or waiting until their immune systems had been degraded by the infection (or the person showed signs of an AIDS-related illness such as pneumocystis pneumonia).
For the couples to participate, the partner had to be HIV-free at the start of the study. Almost all the 1,763 couples were heterosexual (97 percent). The infected partner was male in 890 cases and female in 873.
There was just one new case of HIV among the couples where the HIV-infected partner began immediate antiretroviral therapy. Many different drugs were tested.
"This new finding convincingly demonstrates that treating the infected individual — and doing so sooner rather than later — can have a major impact on reducing HIV transmission," Dr. Anthony Fauci, NIAID's director, said in a statement.
Previous research had suggested early treatment could help. This study put it to a randomized test.
Michel Sidibe, head of the Joint United Nations Programme on HIV/AIDS, called the study a "breakthrough" in a statement. The results underscore the need for access to antiretroviral treatment. One goal of UNAIDS is that there be universal antiretroviral treatment for all eligible people by 2015.