South Africa's HIV data back U=U: 96% stayed below transmission risk at 12 months
A national cohort of 3,584,203 people found that 96.4% of those re-tested still had a viral load below 1000 copies per mL a year later — the threshold at which HIV is not transmitted sexually.
| Group | Value (%) |
|---|---|
| Under 200 copies/mL | 91.1 |
| Under 1000 copies/mL | 96.4 |
The slogan "Undetectable equals Untransmittable" — U=U — rests on a clinical fact: people with an HIV viral load less than 200 copies per mL cannot transmit the virus sexually [s1]. The open question for a public-health programme is not whether suppression blocks transmission, but how durable that suppression is once a person reaches it. A study of South Africa's national HIV programme, published in The Lancet HIV, has now measured that durability at national scale — and the answer is reassuring [s1].
What the study did
Researchers conducted a retrospective observational cohort study using the National Health Laboratory Service National HIV Cohort, a probabilistically linked, de-identified database that captures every viral load test in South Africa's public-sector HIV programme [s1]. They followed individuals aged 15-59 years for 18 months from their first viral load below 200 copies per mL recorded between July 1, 2021, and June 30, 2022 — the baseline [s1].
National guidelines specify annual viral-load monitoring for people suppressed below 200 copies per mL [s1]. So the team asked two questions. First, how many people were actually re-tested — defined as any viral load test 6-18 months after baseline [s1]. Second, what that 12-month result showed, sorted into the 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 [s1].
What it found
The cohort included 3,584,203 individuals — effectively everyone aged 15-59 years with a suppressed viral load in the national programme during the baseline window [s1]. Of these, 2,588,294 (72.2%) were female and 995,909 (27.8%) were male [s1].
Among the full group, 2,858,992 (79.8%) were virally monitored at 12 months [s1]. That re-testing gap matters: a fifth of suppressed people had no follow-up result, so their status a year on is simply unknown.
For those who were re-tested, the picture was strong. Of the 2,858,992 monitored, 2,605,311 (91.1%) had a 12-month viral load below 200 copies per mL, and 2,755,122 (96.4%) were below 1000 copies per mL [s1]. In other words, the overwhelming majority of people who reached suppression and stayed in care were still at zero or almost-zero transmission risk a year later.
Durability was highest among people with an established track record. Those with a previous history of viral suppression had both the highest rates of monitoring — 1,998,198 (87.2%) of 2,291,511 — and of continued suppression below 1000 copies per mL, at 1,950,857 (97.6%) of 1,998,198 [s1]. The groups least likely to stay suppressed were young men, young women, and people with a previous elevated viral load [s1].
Why it matters
South Africa carries one of the world's largest HIV burdens, within a region that dominates the global epidemic. WHO estimates 41.0 million people were living with HIV at the end of 2025, 64% of them in the African Region, and that 95% of people on antiretroviral therapy had suppressed viral loads [s2]. An estimated 570,000 people died of HIV-related causes in 2025 [s2]. Against that backdrop, evidence that suppression holds is not an abstract reassurance — it underpins counselling, prevention messaging and the case for treatment as prevention.
The study's central interpretation is blunt and practical: people with a viral load below 200 copies per mL who remain on antiretroviral therapy still had zero or almost-zero transmission risk 12 months later, and can rely on U=U as a prevention strategy, so long as they stay on treatment [s1]. The authors report that their results were robust to linkage errors and to different outcome definitions [s1].
The caveat in the numbers
The strength of the suppression result sits alongside a weaker monitoring result. Because 79.8% of suppressed people were re-tested, the reassuring 91.1% and 96.4% figures describe those who returned for a test [s1]. The people who fall out of monitoring — disproportionately the young — are the same groups the study flags as least likely to stay suppressed [s1]. Durability of the virus, in other words, is not the only thing that has to hold; so does a person's contact with the health system.
What to watch
Whether South Africa can close the re-testing gap, particularly for young men and women, so that the national picture of durability is not limited to those already engaged in care. And whether the "so long as they remain on antiretroviral treatment" condition at the heart of U=U can be protected as HIV funding tightens globally — the thing that keeps suppression durable is uninterrupted access to the drugs that produce it [s1].
This article is informational and does not constitute medical advice.
Sources
- Durability of HIV viral suppression in South Africa: a national cohort study — The Lancet HIV, 1 August 2026
- HIV and AIDS — Fact sheet — World Health Organization
Sources
- Durability of HIV viral suppression in South Africa: a national cohort study — The Lancet HIV , August 1, 2026
- HIV and AIDS — Fact sheet — World Health Organization
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