Achieving Undetectable Viral Load On ART Renders Individuals Sexually Non-Infectious


PARTNER 2 study reports zero HIV transmissions over 8 years in gay couples who did not use condoms and had achieved an undetectable viral load on HIV treatment.

New results from an international study referred to as PARTNER 2 indicate that achieving an undetectable viral load while on antiretroviral therapy (ART) renders an individual sexually non-infectious. Study results reveal zero HIV transmissions over 8 years in gay men who chose not to use condoms.

The results of the study—deemed the largest study of HIV transmission risk when a sexual partner is infected with HIV and on effective ART—were presented at the AIDS 2018 conference in Amsterdam, Netherlands.

Like the PARTNER 1 study, which ran from 2010 to 2014, in PARTNER 2, held from 2014 to 2018, investigators sought to determine if HIV transmission would occur during unprotected sexual intercourse in serodiscordant partners if the HIV-positive partner was on an effective ART regimen (indicated as having a viral load of <200 copies/mL).

Designed to provide estimates on the risk of transmission from engaging in sexual intercourse without the use of condoms in heterosexual and gay couples, PARTNER 1 found that in 888 couples (548 heterosexual and 340 gay)—where heterosexual couples were estimated to have engaged in condomless sex around 36,000 times, and gay couples reported doing so about 22,000 times&mdash;none of the partners who were originally negative for the virus became positive from having sexual intercourse.

By the end of PARTNER 1, the upper 95% confidence interval for transmission risk in heterosexual couples was 0.46 per 100 couple years of follow (CYFU) and 0.84 per 100 CYFU for gay couples.

Because the majority (65%) of the study population included in PARTNER 1 were heterosexual couples, for PARTNER 2, the investigators sought to provide the same level of evidence for gay couples. Many of the gay couples who were enrolled in PARTNER 1 were also included in the PARTNER 2; new gay couples were also recruited for evaluation. In total, 972 gay couples were enrolled: 480 couples from PARTNER 1 and 492 new couples. A total of 783 couples were deemed eligible for follow-up.

The results of PARTNER 2 indicated that although some of the partners who were originally negative for the virus eventually became positive, none of the cases were found to be linked to their HIV-positive partners, indicating zero cases of HIV transmission between serodiscordant couples.

Due to the larger number of couples, the researchers reported that the upper 95% confidence limit for gay men is now 0.23 per 100 CYFU.

“Despite these couples having sex without condoms almost 77,000 times, we did not find a single case [of infection],” Alison Rodger, MRCP FFPH MSc DipHIV MD, senior lecturer and honorary consultant for infectious diseases and the clinical director of public health at the University College of London, said in a recent statement. “PARTNER 2 data provide robust evidence for gay men that the risk of HIV transmission with suppressive ART is effectively zero, supporting the message of U=U campaign.”

The U=U campaign is working to change the public perception of HIV transmissibility, driving home the fact that if individuals who are HIV-positive take ART as prescribed, on a daily basis, and are able to achieve an undetectable viral load, they will have effectively no risk of sexually transmitting the virus on to an HIV-negative partner. This discovery has significant implications for individuals who are living with HIV, especially those who are in serodiscordant relationships and are thinking about engaging in condomless intercourse or attempting to conceive a child.

Not only do these new results signify a similar level of confidence of the level of risk for gay couples is the same as heterosexual couples, the results further underscore the effectiveness of adhering to an ART regimen.

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