The findings were striking enough that the National Institutes of Health announced Thursday it was stopping the study four years ahead of schedule to get the word out.
Condoms still are crucial for protection. All 1,763 couples in the study, where one partner had HIV and the other didn't, were urged to use them.
But the findings promise to play a role in an important:
Antiviral drugs are life-saving, but also expensive and side effect-prone, so how early should patients start taking them? In the U.S., that's a case-by-case decision for patients whose immune systems so far are moderately damaged by HIV. In developing countries, patients tend to be sicker before treatment starts.
The study may change those guidelines by adding the promise of partner protection.
"It has less to do with a decision about what's good for you from a personal health standpoint than what is the extra added benefit from starting earlier, i.e., transmission, especially if you have a partner who's uninfected," said Dr. Anthony Fauci, director of NIH's National Institute of Allergy and Infectious Diseases, which oversaw the study.
The study randomly divided the couples. Among half, the HIV-infected partner immediately started medication. Among the other half, the infected partner delayed medication until their level of CD4 cells, a key measure of immune health, dropped below 250 or they caught other AIDS-related illnesses.
In 28 couples, the uninfected partner became infected with a strain of HIV that scientists could prove came from the originally infected partner. Only one of those infections was among the early-treated couples, Fauci said.