Using the drug cocktail reduced the likelihood of tranmission by 92 percent, the researchers reported in the journal Lancet.
They said the findings mean the drug cocktails known as antiretroviral therapy, or ART, might be a useful prevention tool as well as a treatment.
“These results are … the strongest evidence to date that ART might decrease HIV transmission risk,” said Dr. Connie Celum, professor of medicine and global health at the University of Washington, who worked on the study.
The team analysed 3,400 couples from seven African countries. In each couple, only one partner was positive for the human immunodeficiency virus, or HIV, which causes AIDS. The team tested couples because they were easier to keep track of.
All of the couples were given counseling on HIV prevention methods, and some were offered HIV drugs when they became available.
During the study, 349 HIV-infected partners were started on HIV drugs. Of the 103 people who became infected during the study, only one caught the virus after the infected partner started taking the drugs.
“These observational data strongly support the hypothesis that ART substantially reduces HIV infectiousness and transmission risk,” Dr. Deborah Donnell of the Vaccine and Infectious Disease Institute at the Fred Hutchinson Cancer Research Center in Seattle and colleagues wrote.
Donnell said the drugs cut the concentration of HIV in the blood to very low levels, which may make people less infectious. In people who took the drugs, the virus was suppressed to very low levels in nearly 70 percent of cases.
A randomised trial was now underway to see if the effect is lasting.
“While awaiting those results, our study indicates that initiation of antiretroviral therapy may have a significant public health benefit as well as clinical advantages for the individuals being treated,” Donnell said in a statement.
She said the findings offer a strong argument for starting treatment for HIV earlier. But even in couples starting treatment late in the disease, the drugs offered benefits.
The AIDS virus infects 33 million people globally and has killed 25 million since the pandemic began in the 1980s. There is no cure and no vaccine but drugs can keep patients healthy.
Without treatment, the virus destroys the immune system, leaving patients susceptible to infections and cancer.
More than 20 drugs are now on the market and can be combined in various ways to control the virus, although it usually mutates eventually and patients must switch to different regimens to keep it under control.
Drugmakers include GlaxoSmithKline, Pfizer, Gilead, Bristol-Myers and Abbott Laboratories. Reuters