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Hadrián Pernas Pardavila

1 Group of Virology and Pathogenesis, Galicia Sur Health Research Institute (IIS Galicia Sur)-Complexo Hospitalario Universitario de Vigo, Vigo, SERGAS-UVigo, Spain. 


In 2000, evidence began to emerge that sexual transmission of HIV was directly related to the viral load of the person infected (Quinn et al. N Engl J Med 2000). This led to the hypothesis that people living with HIV (PLWH) on antiretroviral treatment were less likely to transmit the virus. At that time, mathematical models were published to predict the reduction of HIV transmission in the context of early diagnosis and treatment (Granich et al. The Lancet 2009). This was followed by another observational study showing a significant reduction in HIV transmission between serodiscordant couples after initiation of highly active antiretroviral treatment (Cohen et al. CID 2010; Castilla et al. JAIDS 2005). 


In this context, the first clinical trial to evaluate the impact of early or delayed antiretroviral treatment on HIV transmission was published in 2011. It randomised PWH and serodiscordant couples to early or delayed antiretroviral treatment. It evaluated 1763 couples. There were 39 HIV transmissions in the study, 4 in the early treatment group and 35 in the delayed treatment group. Almost, in relation to the genetic analysis, it was evident that only 28 of 39 transmissions were in the included couples, 1 in the early treatment group and 27 in the delayed treatment group. This shows an 89% reduction in HIV transmission in the serodiscordant couples who started early treatment compared to delayed treatment (Cohen et al. N Eng J Med 2011). In this way, the study makes a new analysis to the next 5 years. During this time, there were 78 infections, of which 46 were related in the couples included, 3 were transmitted in the early treatment group and 43 were transmitted in the delayed treatment group. The risk reduction was 93% in the couples who started treatment early (Cohen et al. N Eng J Med 2016). The main limitation of this trial was the under-representation of men who have sex with men, which was only 2% of the couples included. 


In 2016, the medical journal JAMA had published the first clinical trial to assess HIV transmission during condomless sex between serodiscordant couples on antiretroviral treatment. This study, called PARTNER, included 1166 serodiscordant couples in which the PWH had a low viral load (<200 copies/mL) from 14 European countries. There was an important representation of gay couples (38%). Follow-up was a median of 1 year and 3 months, and it reported a median of 37 sexual acts per year. In total, there were 22000 condomless sexual acts between homosexual couples and 36000 sexual acts between heterosexual couples. During this time, 11 new HIV cases were reported, none of which had a phylogenetic link to his partner's virus and were related to couple-to-couple transmission. The PARTNER study basically shows that serodiscordant couples on antiretroviral treatment and with good virological control who have condomless sex cannot transmit HIV (Rodger AJ et al. JAMA 2016). 


In the PARTNER study, most transmissions were between gay couples (10/11), so an extension was made to better estimate the risk of transmission in these couples. The second phase was called PARTNER2 and was published in The Lancet in 2019. In this case, 782 couples were analysed over 7 years, with a median follow-up of 2 years. A total of 76088 sexual acts were reported. 288 men with HIV in 777 couples (37%) reported condomless sex with another man who was not part of the couple. There were 15 new HIV cases, none of which was phylogenetically related to his partner's virus. The couple had a total of 0 HIV cases (Rodger AJ et al. The Lancet 2019). 


This data has scientifically proven that people living with HIV who are on antiretroviral treatment and have good virological control do not transmit the virus sexually (whether anal or vaginal). Since the publication of the PARTNER trial results is so important in spreading the message of Undetectable = Untransmittable (U=U), it means that it has been shown in some rigorous scientific studies that people living with HIV on treatment and with an undetectable blood viral load do not transmit HIV through unprotected sexual relations (such as condomless sex). This means that antiretroviral treatment is one of the best tools to prevent HIV transmission. This is why early diagnosis of infection is so important in order to start treatment as early as possible and prevent new transmissions. Now that you know this scientific information, it is time to help spread the message. 

Undetectable = Untransmittable: People living with HIV in antiretroviral treatment and viral load undetectable cannot transmit the virus in sexual acts. 

DOI 10.24175/sbd-2024-000009

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