A European study of nearly 1,000 gay male couples who had sex without condoms – where one partner had HIV and was taking antiretroviral drugs to suppress it – has found the treatment can prevent sexual transmission of the virus. After eight years of follow-up of the so-called serodifferent couples, the study found no cases at all of HIV transmission within couples. The study proves, the researchers said, that using antiretroviral therapy to suppress the AIDS virus to undetectable levels also means it cannot be passed on via sex, the researchers said. “Our findings provide conclusive evidence for gay men that the risk of HIV transmission with suppressive ART is zero,” said Alison Rodger, a professor at University College London who co-led the research. She said this “powerful message” could help end the HIV pandemic by preventing the virus’ transmission in high-risk populations. In this study alone, for example, the researchers estimate that the suppressive antiretrovial treatment prevented around 472 HIV transmissions during the eight years.