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U=U gains strength with release of PARTNER2 data

Tobin, Stacey C.

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doi: 10.1097/QAD.0000000000002098
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New data from the PARTNER2 study, reported at the 22nd International AIDS Conference in Amsterdam, bring momentum to the ongoing campaign to equate sustained undetectable viral loads to zero risk of HIV transmission: the U = U campaign.

The possibility that undetectable HIV is untransmittable has been a source of debate for nearly 10 years, ever since the introduction of HAART regimens capable of chronic HIV suppression. Several prospective observational studies have supported this concept. One of the largest of these studies was PARTNER, which monitored seroconversion in more than 1000 serodiscordant heterosexual and homosexual couples in 14 European countries who engaged in unprotected (condomless) penetrative sex [1]. Undetectable viral load in the HIV-positive partner was defined as less than 200 copies/ml while on antiretroviral therapy (ART), measured within the previous 6 months [2]. Notably, individuals taking pre-exposure prophylaxis (PrEP) regimens were excluded from the study. Phylogenetic analysis found that no HIV transmission occurred within couples during the study, who reported more than 58 000 vaginal or anal sex acts during a median follow-up of 1.3 years.

Building on the findings of PARTNER and several other larger epidemiological studies, the Prevention Access Campaign launched the ‘Undetectable = Untransmittable’ or ‘U = U’ campaign in 2016, with the message that individuals who take ART as prescribed to maintain undetectable viral loads will not pass HIV to their partners. The Centers for Disease Control and Prevention subsequently endorsed this concept in a Dear Colleague letter in 2017, noting that ‘When ART results in viral suppression, defined as less than 200 copies/ml or undetectable levels, it prevents sexual HIV transmission’ [3]. Yet, some remained unconvinced, particularly given the decades of messaging around condom use to prevent HIV transmission.

To bolster their initial findings, the PARTNER study investigators continued to collect data from homosexual couples in the PARTNER2 study, with results reported by lead author Dr. Alison Roger in July 2018 [4]. That study included 779 gay couples who reported nearly 75 000 condomless sex acts over a median of 1 year. Again, individuals using PrEP were excluded. Although 17 new infections were detected, none of these were phylogenetically linked HIV transmissions within couples. Thus, the transmission rate between couples was effectively zero, with a 95% confidence interval upper limit of 0.24/100 couple-years of follow-up. Dr. Roger noted that ‘I think the time for excuses are over. I think it is very, very clear that the risk is zero...if you are on suppressive ART, you are sexually noninfectious’.


Conflicts of interest

There are no conflicts of interest.


1. Rodger AJ, Cambiano V, Bruun T, Vernazza P, Collins S, van Lunzen J, et al. Sexual activity without condoms and risk of HIV transmission in serodifferent couples when the HIV-positive partner is using suppressive antiretroviral therapy. JAMA 2016; 316:171–181.
2. Rodger A, Bruun T, Weait M, Vernazza P, Collins S. Partners of people on ART: a new evaluation of the risks (The PARTNER study): design and methods. BMC Public Health 2012; 12:296.
3. Centers for Disease Control and Prevention. Dear colleague: September 27, 2017. [Accessed 14 November 2018].
4. Rodger A, Cambiano V, Bruun T, Vernazza P, Collins S, Corbelli GM, et al. Risk of HIV transmission through condomless sex in gay couples with suppressive ART: the PARTNER2 study expanded results in gay men [abstract WEAX0104LB]. 22nd International AIDS Conference; Amsterdam, The Netherlands; 23–27 July 2018.
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