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Largest study to date shows effective drug treatment prevents HIV transmission in male couples

Published: 03 May 2019

An NIHR-funded European study of nearly 1000 male couples has confirmed that effective antiretroviral therapy prevents HIV transmission, with no cases of transmission within couples over eight years of follow-up.

The PARTNER 2 study is published today in The Lancet. The results provide conclusive evidence that a person with undetectable levels of HIV in their blood cannot transmit the virus through sex.

Couples who took part in the study, funded by NIHR Research for Patient Benefit, were already having sex without using condoms before joining the study. During the course of the study, 15 HIV-negative men became infected with HIV, but not through transmission from their main partner. None of the viruses found in the newly infected men were genetically linked to the HIV virus that had infected their main partner.

The researchers estimate that effective antiretroviral therapy prevented around 472 HIV transmissions during the eight years of the study. They also highlight the importance of regular monitoring for people with HIV and support with long-term adherence to therapy.

NIHR previously funded the earlier PARTNER 1 study through NIHR Programme Grants for Applied Research. PARTNER 1 focused on heterosexual couples, with results in 2016 showing no risk of transmission with undetectable levels of HIV.

The results of both PARTNER studies support the U=U (undetectable = untransmittable) campaign, which was launched to raise awareness of how effective ART can help people have sex without any fear of transmitting HIV. The campaign has been endorsed by more than 780 HIV organisations in 96 countries.

“Our findings provide conclusive evidence for gay men that the risk of HIV transmission with suppressive ART is zero,” says Professor Alison Rodger, who co-led the research.

“Our findings support the message of the international U=U campaign, that an undetectable viral load makes HIV untransmittable. This powerful message can help end the HIV pandemic by preventing HIV transmission, and tackling the stigma and discrimination that many people with HIV face. Increased efforts must now focus on wider dissemination of this powerful message and ensuring that all HIV-positive people have access to testing, effective treatment, adherence support and linkage to care to help maintain an undetectable viral load.”

Professor Sue Ziebland, Programme Director for NIHR's Research for Patient Benefit programme, said "NIHR funded PARTNER 2 and its predecessor to get a definitive answer to the crucial question of whether antiretroviral therapy (ART) could prevent sexual transmission of HIV. These results confirm that when ART is working effectively through continuous treatment, the risk of HIV transmission is effectively zero for gay as well as heterosexual couples (as found in the previous study). This is excellent news that will genuinely change the lives of people with HIV.”

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