People living with HIV are less likely to pass on the virus to their sexual partners when they immediately receive medication.

An international study that included more than 1,700 couples showed that taking antiretroviral (ARV) drugs immediately, instead of waiting for the immune system to be weakened, led to a 96.3% reduction in HIV transmission to a sexual partner who does not carry the virus.

“We’ve speculated for a number of years, in theory, that treating an infected individual should reduce infectiousness to others,” said Dr. Sten Vermund, one of the investigators in the study.

“This was a rigorous clinical trial that proved the concept if you put people on ARVs even before they need it for their own health, it might reduce infectiousness to others.”

Instead of thinking of antiretrovirals strictly as a treatment tool, the medication could also be a prevention tool to curb new infections, said Vermund, who is the director of the Vanderbilt Institute for Global Health.

The study suggests that giving antiretrovirals to someone immediately after infection could first benefit the patient with HIV and reduce the spread to others. The study called HPTN 052, funded by the National Institutes of Health, was scheduled to end in 2015, but the results were released early Thursday because of the clarity of the findings.

"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, director of the National Institute of Allergy and Infectious Diseases, said in a news release.

The study followed 1,763 heterosexual couples from 13 cities in Botswana, Brazil, India, Kenya, Malawi, South Africa, Thailand, the United States and Zimbabwe. The couples were serodiscordant – meaning one person has the HIV, and the other does not have the virus.

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In the study that started April 2005, the HIV-infected partners were randomly assigned to immediately take antiretroviral drugs or to take the drugs when their immunity fell below a certain level or if they experienced an AIDS-related event.

Of the 1,763 couples, 28 new cases of HIV were reported in which their HIV-infected partner was found to be the source of infection. Twenty-seven of the infections were in the group that deferred their antiretroviral therapy. Only one was found in the group that started taking the medication immediately.

“It makes sense,” said Dr. Alvin Friedman-Kien, dermatologist and virologist at New York University Langone Medical Center, who treats HIV/AIDS patients. “The incidence of infected virus would obviously be lowered if you took the antiretroviral medicine. But if I were somebody who had a partner who was HIV positive I wouldn’t take that risk. I would make sure they used condoms and protected sex.”

Friedman-Kien was not involved in the study. He cautioned that even a person on proper antiretroviral therapy could have a few virus particles floating around – and it takes just one virus particle to infect another person.

The concept that a patient should immediately take antiretrovirals after diagnosis has already been proposed by public health officials in San Francisco, California, and Vancouver in Canada. But, many in America as well as developing countries cannot get access to the medications despite having dire medical needs.

CNN's Elizabeth Landau contributed to this report.