Results of a new study into men in same-sex relationships whose HIV statuses differ have been published showing the effectiveness of treatment as prevention.

The study, which was led by the University of New South Wales Kirby Institute, was published in medical journal The Lancet.

Titled Opposites Attract, the study contributes to global evidence demonstrating that when the HIV-positive partner is on daily antiretroviral therapy (ART) and has an undetectable viral load, the risk of sexual transmission to the HIV-negative partner is effectively zero.

“Opposites Attract shows that HIV treatment as prevention works,” the study’s project leader Dr Benjamin Bavinton said.

“Not only is this information vital to inform HIV prevention in gay, bisexual, and other men who have sex with men, it provides strong evidence to help dismantle some of the stigma still associated with HIV.”

Researchers followed the sexual behaviour of 343 serodiscordant couples across Australia, Brazil and Thailand across four years.

The study involved specifically tracking acts of condomless anal intercourse, along with testing the HIV-negative partner for HIV, and the HIV-positive partner’s viral load.

The research charted over 12,000 acts of anal intercourse where the HIV-negative partner was not taking PrEP and the HIV-positive partner was virally suppressed, or undetectable.

During that time, there was no new infections between Opposites Attract study partners.

There were 3 new HIV infections in that time, but none were phylogenetically-linked – meaning that scientists analysed samples from each partner and determined the infections did not occur within the couple.

The data was first presented at the IAS Conference on HIV Science in Paris last year, adding to a very limited body of evidence which largely includes the PARTNER Study, which showed the same outcome in 2016.

“These results form a significant part of the evidence base for the international community-led Undetectable=Untransmissible, or U=U campaign,” said the Professor Andrew Grulich, chief investigator on the study.

“[The results] highlights the fact that people living with HIV can now live long and healthy lives, with effectively zero chance of sexually transmitting the virus to others, provided their viral load is undetectable due to effective ART.”

Research recently found that while most gay and bisexual men are comfortable relying on PrEP for HIV prevention, far fewer are aware of the effectiveness of treatment as prevention.

“Even though people living with HIV have known for years that we are not at risk of passing on HIV if we have an undetectable viral load, there is still so much stigma and fear attached to HIV,” The Institute of Many’s co-founder Nic Holas said earlier this year.

“It’s not enough for us to be confident that we are protecting our partners.

“Our partners and potential partners also need to understand that undetectable viral load means there is absolutely no risk of them contracting HIV.”

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