The Kirby Institute’s Opposites Attract study, the second of its kind in the world after the PARTNER study in Europe and the UK, has concluded that condomless sex with a person living with HIV, who has sustained an undetectable viral load for six months or more is an effective form of safe sex.
The Opposites Attract study was an observational study of male gay serodiscordant couples – that is, relationships where one partner is HIV positive and one partner is HIV negative. It was conducted in Australia, Brazil and Thailand.
The key research question of the study was: To what extent do HIV treatments in the HIV positive partner reduce the risk of HIV transmission to the HIV negative partner in these couples?
The study began recruiting in early 2012 and followed 358 couples over four years. The result is that these couples had almost 17,000 acts of sex without a condom, none of which resulted in HIV transmission.
Opposites Attract is one of only two studies ever to be conducted that explores this research question in gay men. The other study – PARTNER – is ongoing in Europe and the UK. In July 2016, the PARTNER study reported its phase one results, showing that there were no HIV transmissions within serodiscordant couples where the HIV positive partner had an undetectable viral load and who were having sex without condoms with each other. And this was after an estimated 58,000 separate occasions of condomless sex.
Undetectable = Safe | Emen8
There were no “linked” HIV transmissions in the Opposites Attract couples. A “linked” transmission is where genetic analysis of the virus shows that the HIV came from the HIV positive partner in the couple to his HIV negative partner. So, no HIV negative man in the study contracted HIV from his HIV positive study partner.
There were over 12,000 reported acts of anal sex that were protected only by undetectable viral load (that is, condomless anal sex when the HIV negative partner was not taking PrEP), and there were still no linked transmissions. This indicates that condomless sex with an undetectable viral load is safe.
PARTNER is currently running phase two of its study, which involves a larger number of gay couples. The final results will be reported in the next couple of years.
Opposites Attract enrolled gay male serodiscordant couples in three Australian cities – Sydney, Melbourne, and Brisbane; as well as in Rio de Janeiro, Brazil, and Bangkok, Thailand. The couples were followed up over time, visiting their study clinic at least two times per year.
“‘Undetectable virus level effectively prevents HIV transmission among gay couples,’ said Professor Andrew Grulich from the Kirby Institute and chief investigator on the study.”
While the couples needed to be having regular anal sex with each other to enrol, there were no requirements about condom use; some couples always used them, while others sometimes or never used them. There were also no restrictions on whether or not the HIV negative partner could use pre-exposure prophylaxis (PrEP). So, this meant that the study was a good representation of what HIV prevention in sexually-active male serodiscordant couples looks like in the real world today.
“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.”
In gay and heterosexual couples, 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 an undetectable viral load.
Opposites Attract reinforces the findings of the PARTNER study and gives confidence that maintaining an undetectable viral load is an effective HIV prevention strategy. An undetectable viral load also increases health benefits for those living with HIV.
However, it is important to remember that when the HIV positive partner is in the first six months of starting HIV treatment, it can take time for the viral load to become undetectable. There have been some cases overseas in heterosexuals where transmission happened when the HIV positive partner was on treatment but was not yet undetectable. So, during the first six months of treatment and until the viral load is undetectable, it is best to use condoms or for the HIV negative partner to take PrEP.
The study was coordinated by the Kirby Institute at the University of New South Wales, in Sydney, Australia.