PARTNER2 Study Confirms “Undetectable Equals Untransmittable”

PARTNER2 Study Confirms “Undetectable Equals Untransmittable”

On Wednesday, July 25, 2018, at the International AIDS Society Conference in Amsterdam, The Netherlands (IAS2018), researchers presented the results of the PARTNER2 Study, confirming that viral suppression prevents HIV transmission in serodifferent gay male couples.

Building on previous studies, including the PARTNER1 Study and Opposites Attract, the PARTNER2 study sought to provide precise estimates of the risk of HIV transmission during condomless sex among “serodifferent” gay male couples (i.e., one partner is HIV-positive, the other is HIV-negative) when the HIV-positive partner’s viral load has been rendered undetectable through antiretroviral treatment. Previous studies had found no cases of HIV transmission in these kinds of couples, but the amount of statistical confidence available had remained less than that for heterosexual couples.

Carl Dieffenbach, Bruce Richman, Alison Rodger, Mike Cohen, and Pietro Vernazza.
Photo courtesy Prevention Access Campaign

The PARTNER2 results showed conclusively that despite almost 75,000 condomless sex acts, there were zero cases of HIV transmission between the partners. Alison Rodger of University College London reported that these results indicate a precise rate of zero for within-couple HIV transmission.

The study enrolled 972 serodifferent gay couples in fourteen European countries. Couples were eligible if they reported condomless sex, if the HIV-negative partner did not report using pre- or post-exposure prophylaxis (PrEP or PEP), and if the HIV-positive partner was virally suppressed.

Matthew Hodson, the Executive Director of NAM aidsmap, the HIV/AIDS information resource, remarked to A&U, “IAS2018 will be remembered as the conference when ‘U Equals U’ moved from being an activist rallying cry to the scientifically established position. HIV stigma remains a public health crisis resulting, in extreme cases, in murder and suicide. It should be a public health duty to inform all of us who are living with the virus, and all of those whom we encounter, that effective HIV treatment prevents transmission.

“The knowledge that U equals U… offers freedom from the fear of passing the virus on to those that we love and those that we desire [and] has the power to encourage people to test and to remain adherent to their treatment. [It also] gives us the impetus to demand viral suppression as a right for all people living with HIV.

“This is the moment when facts must conquer fear. This is the moment when science must trump stigma,” he concluded.

Bruce Richman, Founding Executive Director of the Prevention Access Campaign, the powerhouse behind U=U, also had high praise for the study. “PARTNER2 provided even more evidence on top of overwhelming evidence to support U=U. It was the frosting on the cake. [It] closes the chapter on whether MSM anal sex is any riskier than vaginal sex.”

Richman had especially high praise for Alison Rodger. He told A&U, “Alison Rodger did something so unusual and wonderful. At the end of her press conference and presentation, she confirmed that the research supports U=U and acknowledged the Prevention Access Campaign for our work to ensure the body of evidence reaches the public. That meant so much to my colleagues and me. It was so respectful. And she put the data into a real-world context. This is above and beyond what researchers typically do. I’m so grateful to her and the partner executive committee.”

For more information about NAM aidsmap, please check out More information on the U=U campaign can be found at To view Mr. Richman’s question to Ms. Rodger at her press conference, and her response, go to:

—Reporting by Hank Trout

Hank Trout, Editor at Large, edited Drummer, Malebox, and Folsom magazines in the early 1980s. A long-term survivor of HIV/AIDS (diagnosed in 1989), he is a thirty-eight-year resident of San Francisco, where he lives with his fiancé Rick Greathouse. Follow him on Twitter @HankTroutWriter.