A study funded by the National Institute for Health Research has shown that viral suppression may eliminate human immunodeficiency virus (HIV) transmission through condomless sex in gay men. The study’s results are similar to a previous discovery for heterosexual couples.

Results of the recent study, published in The Lancet, support the benefits of early testing and treatment for HIV, as well as the message of Prevention Access Campaign’s U=U (undetectable equals untransmittable) initiative.

The PARTNER study was a prospective observational study conducted at 75 sites throughout Europe. The first phase of the study (Sept 15, 2010, to May 31, 2014) recruited and followed up both heterosexual and gay couples with an HIV-positive partner taking suppressive antiretroviral therapy (ART) and who reported condomless sex. The study’s extension (to April 30, 2018), PARTNER2, recruited and followed up only gay couples.

Between Sept 15, 2010, and July 31, 2017, 972 gay couples were enrolled in the study, of which 782 couples generated 1593 eligible couple-years of follow-up, according to the report. During study visits, data was collected from these couples, which included sexual behavior questionnaires, as well as HIV testing for the HIV-negative partner, and HIV-1 viral load testing for the HIV-positive partner.

Study participants reported condomless anal sex 76,088 times. Thirty-seven percent of 777 HIV-negative men reported condomless sex with other partners, and 15 new HIV infections occurred during eligible couple-years of follow-up. However, none of the new HIV infections were phylogenetically linked within-couple transmissions, resulting in an HIV transmission rate of zero (upper 95% CI 0·23 per 100 couple-years of follow-up).


Risk of HIV transmission through condomless sex in serodifferent gay couples with the HIV-positive partner taking suppressive antiretroviral therapy (PARTNER): final results of a multicentre, prospective, observational study. The Lancet. DOI:https://doi.org/10.1016/S0140-6736(19)30418-0. Published May 2, 2019. Accessed May 8, 2019.