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The PARTNER 2 Study and Undetectable = Untransmittable (U=U)

The chance of any HIV-positive person with an undetectable viral load transmitting the virus to a sexual partner is "scientifically equivalent to zero," according to presenter, Dr. Alison Rodger, University College, London. Final results from the PARTNER study were presented on the opening day of AIDS 2018.  Results originally announced in 2014  from the first phase, PARTNER 1, already showed that “Undetectable = Untransmittable” (U=U). However, because of the population distribution in PARTNER 1, the study team continued the trial to ensure the relevance of the data in gay men, and for anal sex.

The final results from PARTNER 2, the second phase, which only recruited gay couples, that were presented in Amsterdam indicate, in the words of the researchers: “A precise rate of within-couple transmission of zero” for gay men as well as for heterosexuals. Note the qualifier – “within couple transmission.” The PARTNER study recruited HIV mixed status couples (one partner HIV positive, one negative) at 75 clinical sites in 14 European countries. They tested the HIV-negative partners every 6-12 months for HIV, and followed viral load in the HIV-positive partners. Both partners also completed behavioral surveys. In cases of HIV infection in the negative partners, their HIV was genetically analyzed 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.

Why PARTNER matters:
The results of PARTNER 2 were reported on the tenth anniversary of a contentious debate at the 2008 Mexico City International AIDS Conference on the validity of "The  Swiss Statement." The statement from The Swiss Federal Commission for HIV/AIDS was the first published statement to say that, under defined circumstances, people with HIV who have fully suppressed viral loads due to antiretroviral treatment cannot transmit HIV.

At the time it was said that due to lack of viral load monitoring in anything but high-income countries, this fact – even if true – would have little relevance to most people with HIV. Also, serious concerns arose that telling people with HIV that they were not infectious if virally suppressed would be counter-productive because it would discourage safer sex, especially condom use. The more important message to give to people, some experts said, was that they should take every dose of their therapy.

The U=U (Undetectable equals Untransmittable) campaign did not exist at the time and  was founded later as a reaction to these positions.The thinking behind U=U is that telling people they are not infectious if virally suppressed was a message of hope, and something desired by many people with HIV. It would help to combat the stigma against them, and their own self-stigma. By providing a powerful incentive to take treatment it could also have a positive impact on public health, as well as on individuals. The Swiss Federal Commission apologized at the time that stating that people “do not” transmit HIV under the circumstances above was too definite, and that they had only meant to indicate that the likelihood of transmission was reduced. But what PARTNER tells us is that the Swiss Commission was right all along. People who are virally suppressed do not transmit HIV.

It was widely assumed at the time that sexually transmitted infections (STIs) might make people infectious even when they normally had an undetectable viral load. But PARTNER tells us that STI infections have no impact on HIV infectiousness in people who are fully suppressed. And it was thought that because HIV is transmitted more easily via anal than vaginal sex, the results might not hold for gay men. Again, PARTNER 2 now tells us that U=U holds just as strongly for gay men (and for anal sex) as for heterosexuals.

About PARTNERS 1 and 2:
PARTNER 1 was conducted from September 2010 - May 2014, and PARTNER 2 from May 2014 - April 2018. There were 888 couples in PARTNER 1, 337 (38%) were gay couples. In PARTNER 2, another 635 gay couples were recruited, making a total of 972 gay couples and 516 heterosexual ones in the whole study. Couples only contributed to the data if they had had condomless sex since the last data collection point, if the HIV-positive partner had maintained a viral load under 200 copies/ml throughout, and if the HIV-negative partner had not used pre-exposure prophylaxis (PrEP) or post-exposure prophylaxis (PEP). In summary, 783 male/male couples up provided 1596 couple-years of data, with an average eligible time in the study of 1.6 years. Couples reported on average 43 acts of condomless sex a year. At baseline, the average age of the HIV-negative partners was 38 and of the HIV-positive ones, 40. They reported having had condomless sex with each other for an average of a year before joining the study. The HIV-positive partners had been on antiretroviral therapy for an average of four years. Ten per cent of the negative partners and 14% of the positive ones were diagnosed with an STI during the study. The 1596 couple years, containing an estimated total of 76,991 condomless sex acts, produced no transmission between partners. There were 15 new infections – but three-quarters of them reported recent condomless sex with a different partner, and genotyping of the HIV transmitted showed that none of these infections came from the regular partner; six had a completely different subtype of HIV. Altogether, 285 of the HIV-negative men (37%) reported condomless sex with other men.

What has changed is that we can now state that U=U with at least as much confidence for gay men as we already could for heterosexuals or, as the investigators say, “PARTNER 2 provides a similar level of confidence for gay men as for heterosexual indicated in PARTNER 1.” Dr. Rodger noted further, “We looked so hard for transmissions. And we didn’t find any.”

PARTNERS 2: Rodger A et al. Risk of HIV transmission through condomless sex in gay couples with suppressive ART: the PARTNER 2 study expanded results in gay men. 22nd International AIDS Conference, Amsterdam, abstract WEAX0104LB, 2018.

Source: Reporting from Amsterdam for PRN News: Bill Valenti, MD

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