An end to the scourge of Aids could be in sight after a study found that men with HIV who were taking antiretroviral drugs did not pass on the disease.
Researchers tested 1000 couples and found no cases of transmission over eight years.
It could mark the first step in beating a disease considered a death sentence when it was discovered in the 80s.
University College London’s Alison Rodger, who co-led the research, said: “This powerful message can help end the HIV pandemic by preventing transmission, and tackling the stigma and discrimination many people with HIV face.”
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The study, published in The Lancet journal, centred on 1000 male couples in which one partner was HIV positive and taking antiretroviral drugs to suppress the virus, and the other was HIV negative.
The couples had sex with no condoms around 77,000 times over eight years.
The researchers said 472 transmissions of HIV would have been expected without treatment.
Fifteen men were infected with HIV but DNA testing showed the virus did not come from their main partner.
The scientists added that the treatment proved as effective for gay couples as it did for straight couples.
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Dr Michael Brady, of HIV charity Terrence Higgins Trust, said it was “impossible to overstate the importance of these findings”.
He added: “The study has given us the confidence to say people living with HIV who are on effective treatment cannot pass the virus to their sexual partners.”
Since the start of the Aids pandemic, 77million people have become infected with HIV. Almost half – 35.4million – have died of Aids.
