The final results from the PARTNER2 trial, the largest study to analyze HIV treatment as prevention among men who have sex with men, offered a trove of new evidence indicating that people with HIV who have an undetectable viral load thanks to antiretroviral treatment do not transmit the virus. In fact, the study’s lead author, Alison Rodger, MD, of University College London, called the risk of transmission “zero” in this context. There were no transmissions within 782 mixed-HIV-status European gay male couples who collectively had condomless sex some 76,000 times. This new data set—together with the findings of two other studies, called HPTN 052 and Opposites Attract, as well as an earlier phase of the PARTNER study—have collectively provided a massive amount of evidence regarding transmission risk within both male-male and male-female mixed-HIV-status couples. All this research firmly supports the global consensus that undetectable equals untransmittable, or U=U.