Durability of HIV viral suppression in South Africa: a national cohort study.

backgroundPeople with an HIV viral load less than 200 copies per mL cannot transmit HIV sexually, but viral rebound can lead to transmission risk. We aimed to quantify 12-month durability of viral suppression in South Africa's national HIV programme.

methodsWe conducted a retrospective observational cohort study to assess the 12-month durability of viral suppression in South Africa's National Health Laboratory Service National HIV Cohort, a probabilistically linked, de-identified database including all viral loads in the public sector HIV programme. Individuals aged 15-59 years were followed up for 18 months from their first viral load less than 200 copies per mL occurring between July 1, 2021, and June 30, 2022 (baseline). Guidelines specified annual monitoring if viral load was less than 200 copies per mL. The first outcome of our study was viral monitoring at 12 months, defined as any viral load test 6-18 months after baseline. The second outcome of our study was 12-month viral load, categorised according to WHO transmission risk thresholds: less than 200 copies per mL (zero risk), 200-999 copies per mL (almost zero risk), and 1000 copies per mL or greater. We fit modified Poisson regression models to assess predictors of these outcomes.

findingsOur study included 3 584 203 individuals, reflecting all people living with HIV aged 15-59 years with an HIV viral load less than 200 copies per mL in the national HIV programme between July 1, 2021, and June 30, 2022. 2 588 294 (72·2%) individuals were female and 995 909 (27·8%) individuals were male. Of the 3 584 203 individuals with a baseline viral load less than 200 copies per mL, 2 858 992 (79·8%) were virally monitored at 12 months. Of those, 2 605 311 (91·1%) had a 12-month viral load less than 200 copies per mL, and 2 755 122 (96·4%) had a 12-month viral load less than 1000 copies per mL. Individuals with a previous history of viral suppression had the highest rates of monitoring (1 998 198 [87·2%] of 2 291 511 individuals) and continued suppression at less than 1000 copies per mL (1 950 857 [97·6%] of 1 998 198 individuals). Those least likely to remain virally suppressed included young men, young women, and people with previous elevated viral loads. Results were robust to linkage errors and different outcome definitions.

interpretationPeople with viral load less than 200 copies per mL who remained on antiretroviral therapy still had zero or almost zero transmission risk 12 months later. People living with HIV with viral load less than 200 copies per mL can rely on Undetectable=Untransmittable as a prevention strategy, so long as they remain on antiretroviral treatment.

fundingUS National Institutes of Health.