HIV-suppressing medication can make the AIDS virus 'untransmittable' even among couples who have s3x without condoms, new research showed today.
A Europe-wide study monitored nearly 1,000 gay male couples over eight years, where one partner was HIV-positive and receiving antiretroviral (ART) treatment, while the other was negative.
Doctors did not find one single case of in-couple transmission within that time.
This raises hopes that widespread ART programmes could eventually end new infections.
'Our findings provide conclusive evidence for gay men that the risk of transmission with suppressive ART is zero,' said Alison Rodger, from University College London, who co-lead the research published in The Lancet.
'They support the message... that an undetectable viral load makes HIV untransmittable. This powerful message can help end the HIV pandemic by preventing transmission, and tackling the stigma and discrimination that many people with HIV face.'
The study alone, the researchers estimate, helped to prevent around 472 HIV transmissions during the eight years.
More than 21 million people currently receive regular ART medication, which suppresses the virus - only around 59 percent of global sufferers.
The authors of the study noted several limitations, including that the average age of the HIV-negative men was 38. Most transmissions occur in people aged under 25.
Individuals currently on ART must take medication almost every day for the rest of their lives, and treatment is often disrupted for a variety of reasons.
But the fact that couples can have unprotected s3x for years without passing on the virus was still worth noting, experts said.
'Timely identification of HIV-infected people and provision of effective treatment leads to near normal health and virtual elimination of the risk of HIV transmission,' said Myron Cohen, from the UNC Institute of Global Health and Infectious Diseases.
'Yet maximising the benefits of ART has proven daunting: fear, stigma, homophobia, and other adverse social forces continue to compromise HIV treatment.'
Its findings add to an earlier phase of the study which looked at HIV transmission risk for serodifferent heteros3xual couples in the same circumstances. It also found zero risk.
While 15 of the men among the 972 gay couples in this phase did become infected with HIV during the eight years of follow-up, genetic testing showed their infections were with strains of HIV acquired from another s3xual partner.
HIV and the fatal illnesses it provokes remain one of the world's largest health crises despite much progress in recent years.
Since the start of the AIDS epidemic in the 1980s, more than 77 million people have become infected with HIV. Almost half of them - 35.4 million - have died of AIDS.
Global health experts say the fight against HIV is at a precarious point, with the annual number of AIDS deaths falling and the number of people getting antiretroviral treatment rising, but the number of new infections stubbornly high at around 1.8 million new cases a year worldwide.
-Daily mail