Effective HIV treatment halts HIV transmission among homosexual couples, study finds

News | Published on 25 Jul 2017

Paris, France – 25 July 2017 Results from the largest study to analyse HIV transmission risk among homosexual couples with differing HIV status have shown that HIV positive men who are on treatment that makes the virus undetectable, do not transmit HIV to their partners.

The results from the Kirby Institute’s Opposites Attract study were presented today at the IAS Conference on HIV Science in Paris.

During the course of the study, participant couples reported almost 17 thousand acts of anal-intercourse without a condom, none of which resulted in HIV transmission.

“Undetectable virus level effectively prevents HIV transmission among gay couples,” said Professor Andrew Grulich from the Kirby Institute and chief investigator on the study. “Opposites Attract is the first study to show that these results apply in both high and middle income countries. Our research adds to the evidence from a small number of other international studies of heterosexual and homosexual couples and means that we can say, with confidence, that effectively treated HIV blocks transmission in couples of differing HIV status.”



HIV treatment works by suppressing the level of virus in a person living with HIV’s body, so that immune system damage is halted and even reversed. When treatment is consistently taken daily, the virus levels become so low that they become undetectable in the blood. The results of Opposites Attract show that when an undetectable viral load is maintained, the risk of HIV transmission is negligible.

“This is life-changing news for couples of differing HIV status. But it is important that the HIV positive partner is under regular medical care and does not miss any of their anti-retroviral medication in order to ensure they maintain an undetectable viral load” said Professor Grulich. “Our data add to previous studies which show that there has never been a recorded case of HIV transmission from an HIV-positive person to their HIV-negative sexual partner when the HIV-positive partner had undetectable viral load.”

Opposites Attract was a cohort study of HIV transmission among 358 gay couples in relationships where one partner is HIV positive and the other negative. The study followed participants from Thailand, Brazil and Australia over four years from 2012–2016.

“We are grateful to the participant couples who were involved in the study, as well as our study partners from Evandro Chagas Clinical Research Institute, Fiocruz in Brazil and the Thai Red Cross in Thailand,” said Professor Grulich. “The international collaboration made possible through our partnerships adds to the strength and validity of these very exciting study results.”

The majority of this study is funded by the National Health and Medical Research Council (NHMRC). A two year extension was made possible by the Foundation for AIDS Research (amfAR), ViiV and Gilead.


Stakeholder quotes:
“Demonstrating that condomless sex with undetectable viral load is a form of safe sex does not only prove the scientific concept of treatment as prevention but heavily destigmatises gay men living with HIV, as well as their seronegative partners, in Thailand. Condomless sex with partners outside of the relationship is obviously very common and this should immediately alert health care providers of the urgency of PrEP for Thai men who have sex with men.”
Dr Nittaya Phanuphak, PhD, MD, Chief of the Prevention Department at the Thai Red Cross AIDS Research Centre.
“The results of the Opposites Attract study have important implications for serodiscordant couples in Brazil, and all around the world. Opposites Attract has shown us that maintaining undetectable viral load prevents HIV transmission - an important finding that will help to break down stigma associated with living with HIV. These results strengthen the argument for treatment as prevention and provide couples with options when it comes to negotiating safe sex. The Evandro Chagas Clinical Research Institute is proud to be a part of this very important endeavour.”
Dr Beatriz Grinsztejn, Evandro Chagas Clinical Research Institute, Fiocruz
As HIV continues to disproportionately affect gay men and other men who have sex with men worldwide, the results of this study are extremely encouraging and underscore the need to get people tested and onto treatment immediately if they are HIV positive. This important breakthrough underscores yet again how investments in HIV research yield invaluable dividends in the global response to HIV.”
Kevin Robert Frost, Chief Executive Officer amfAR
“These results are so important for loving couples wishing to negotiate the intimacy they share. As a clinician, there is nothing more helpful than discussing with our clients knowing our comments are based in rigorous science.”
Professor Kit Fairley, Melbourne Sexual Health Centre & Monash University
"The Opposites Attract Study is ground-breaking Australian research. The use of undetectable viral load (UVL) in sexual decision making is becoming increasingly common for gay men in NSW and across Australia. The results of this study are vital in confirming the effectiveness of this prevention method. Sex in the context of UVL is safe sex, as is sex in the context of condoms or PrEP. When seen alongside recent research findings demonstrating the important individual health impacts of early treatment and systemic changes such as the removal by the NSW Government of the co-payment for HIV treatments, people with HIV have more reasons than ever to treat HIV rapidly after diagnosis."
Nicolas Parkhill, Chief Executive Officer, ACON
“The results from this study have the ability to change not only the ways in which many PLHIV view themselves but importantly how others view people living with HIV (PLHIV). PLHIV have accepted the stinging pain of rejection and discrimination for years. Now, based on proven scientific evidence, we can let go of some of the fear and anxiety and feel confident that the sex we negotiate with our partners cannot inadvertently result in an HIV infection. The challenge ahead is to get this information and the effectiveness of treatment as prevention (TasP) into the minds of the community and dismantle the stigma that continues to thwart our efforts to get people to test frequently and start treatment early.”
Brent Allen, CEO, Living Positive Victoria 


Luci Bamford, Media and Communications Manager, Kirby Institute


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