according to a new paper published in the Lancet.
The prospective observational PARTNER2 study (Lancet 2019 May 2.) followed 782 serodiscordant gay couples from 14 European countries, where the HIV-positive partner had to be virally suppressed to below 200 copies of HIV-1 RNA per milliliter, and the couple was engaging in condomless sex without using pre- or postexposure prophylaxis.
After a median follow-up of 2 years, there was not a single case of HIV transmission between couples, representing a transmission rate of zero. The study did record 15 new HIV infections during follow-up but these were all phylogenetically linked to sources other than the HIV-positive partner.
The HIV-positive partners had been on antiretroviral therapy for a median of 4.3 years – most on regimens of three or more drugs – with high levels of adherence. During the follow-up period, 37 HIV-positive partners (5%) reported missing their antiretroviral therapy for more than 4 consecutive days.
“Our results give equivalence of evidence for gay men as for heterosexual couples and indicate that the risk of HIV transmission when HIV viral load is suppressed is effectively zero for both anal and vaginal sex,” wrote Dr. Alison J. Rodger of the Institute for Global Health at University College London, and coauthors. “These findings emphasize the importance of regular monitoring to ensure HIV viral load remains suppressed and supporting HIV-positive people with long-term adherence.”
Around one-quarter of the HIV-negative men and 27% of the HIV-positive men reported a sexually-transmitted infection during follow-up; the most common infections were syphilis, gonorrhea, and chlamydia.
The study noted six additional cases of seroconversion of HIV-negative partners. However, these occurred outside the eligible couple-years of the follow-up period. They were ineligible due to no questionnaire about sexual behavior having been completed by either partner in the couple, a lack of condomless sex between the couple, use of postexposure prophylaxis, or a lack of viral load measurement for the HIV-positive partner in the past year.
The authors did note that the study population was predominantly white and with a median age of 38 years, while most HIV transmission occurs in young people aged under 25 years.
“The results from the PARTNER studies support wider dissemination of the message of the U=U [Undetectable equals Untransmittable] campaign that risk of transmission of HIV in the context of virally suppressive ART is zero,” they wrote.
The study was supported by the National Institute for Health Research, the British HIV Association, the Danish National Research Foundation, ViiV Healthcare, Gilead Sciences, Augustinus Fonden, and A P Møller Fonden. Fourteen authors declared grants, personal fees and other support from the pharmaceutical sector.