Any HIV-positive person with an undetectable viral load transmitting the virus to a sexual partner is scientifically equivalent to zero, researchers confirmed at the 22nd International AIDS Conference (AIDS 2018) in Amsterdam today.

Final results from the PARTNER 2 study were presented this morning at a press conference on the opening day of AIDS 2018, and they were specifically in relation to gay men.

Results originally announced in 2014 from the first phase, PARTNER 1, already indicated that Undetectable equals Untransmittable (U=U). However, the statistical certainty of this result was not quite as convincing in the case of gay men, or for anal sex, as it was for vaginal sex.

PARTNER 2, the second phase only recruited gay couples. The results indicate, in the words of the researchers, “A precise rate of within-couple transmission of zero” for undetectable gay men as well as for heterosexuals.”

The PARTNER study recruited HIV serodiscordant couples (one partner positive, one negative) at 75 clinical sites in 14 European countries. They tested the HIV-negative partners every six to 12 months for HIV, and tested viral load in the HIV-positive partners. Both partners also completed behavioural surveys. In cases of HIV infection in the negative partners, their HIV was genetically analysed to see if it came from their regular partner.

The study found no transmissions between gay couples where the HIV-positive partner had a viral load under 200 copies/ml – even though there were nearly 77,000 acts of condomless sex between them.

Yesterday, at a pre-conference event, the Australasian Society for HIV, Viral Hepatitis and Sexual Health Medicine (ASHM) released a new guide to help doctors in Australia understand the ‘Undetectable=Untransmittable (U=U)’ message.

“This is a global first in the HIV response plugging a crucial gap in guidance for clinicians who need to better informed but also properly guided to give accurate and evidence-based information to their patients,’ Scott McGill, director of Programs at ASHM, told Gay Star News.

“There was keen interest from a number of countries from Canada to Zimbabwe who also talked about similar issues that clinicians in those settings faced.”

ACT UP Dublin has called on the Irish Government to respond to the PARTNER 2 study by putting similar messaging about Undetectable Equals Untransmittable into action.

“The HSE put out a booklet last year about treatments for HIV and it sort of danced around Undetectable Equals Untrasmittable. They told us they were waiting for the results of the PARTNER 2 results before they fully got behind the U=U message,” said Andrew Leavitt of ACT UP. “So now that those results have come out and have confirmed what every other study has shown, we expect them to start incorporating the U=U message into all of the materials talking about HIV.

“It’s a really important aspect of HIV treatment, prevention and messaging, and most importantly what’s communicated to people living with HIV. There must be clear messages supporting U=U from the HSE.”