For the roughly 39 million people living with HIV worldwide, daily antiretroviral therapy has been transformative — turning a once-fatal infection into a manageable chronic condition. But the medication must be taken every day, for life. Stop taking it, and the virus rebounds — typically within weeks.
That may be about to change.
At the Conference on Retroviruses and Opportunistic Infections (CROI 2026) — the world's most prestigious HIV research meeting — a team from the University of Oxford presented results from the RIO trial that have quietly rocked the field: more than half of the participants who received two infusions of broadly neutralising antibodies (bNAbs) achieved prolonged viral remission after stopping their HIV medication entirely. Two of those participants have now been off antiretroviral therapy for more than a year.
One of them has had a completely undetectable viral load throughout that entire period.
**What Are Broadly Neutralising Antibodies?**
Broadly neutralising antibodies are large proteins produced by the immune system that are capable of targeting and disabling a wide range of HIV strains — not just a single variant. In people with HIV, these antibodies are either absent or insufficient to control the virus on their own. The RIO trial tests whether infusing patients with two powerful lab-produced bNAbs — teropavimab and zinlirvimab — can change that equation.
The RIO B phase, presented at CROI 2026, enrolled 28 participants who had initially received a placebo in the earlier phase and had quickly experienced viral rebound when stopping ART. These weren't easy cases — these were people whose immune systems hadn't previously been able to suppress the virus without medication.
Each participant received two infusions of the bNAb combination, 20 weeks apart, while still on their regular ART. After waiting six months for the antibodies to clear their system, they stopped taking HIV medication.
What happened next was unexpected.
**The Results**
Of the 28 participants, **15 (54%) had not experienced viral rebound 20 weeks after stopping ART** — a period during which, historically, 95% of people who stop treatment rebound within just six weeks.
Six participants remained suppressed at week 39. Five maintained low or undetectable viral loads for a full year. And two remain off ART after more than a year — with one maintaining a completely undetectable viral load the entire time.
These are not numbers that come from direct viral suppression by the antibodies. By the time the participants stopped ART, the infused antibodies had largely cleared their systems. Something else was keeping the virus in check.
**A 'Vaccinal Effect'**
Professor John Frater, the trial's co-principal investigator at Oxford, described it as a **"vaccinal effect"** — a phenomenon where the antibodies appear to have triggered lasting immunological changes that allow the participant's own immune system to continue controlling the virus long after the antibodies themselves are gone.
In effect, the bNAbs may be doing something closer to training the immune system than simply treating the infection. They appear to stimulate new HIV-specific T cells — immune cells capable of recognising and attacking infected cells — that persist after the antibody infusions end.
'The delayed rebound we're observing suggests the antibodies induced lasting immunological changes, rather than directly suppressing the virus,' Frater explained at CROI 2026.
This shifts the conceptual framework for HIV cure research significantly. Where previous approaches focused on eliminating the hidden viral reservoir — the 'tank' of dormant infected cells that persists even on ART — the RIO findings suggest a different possibility: teaching the immune system to control what remains.
**Context: How Remarkable Is This?**
To appreciate what these numbers represent, consider the baseline: **95% of people who stop antiretroviral therapy experience viral rebound within six weeks**. The immune system alone, without external support, cannot suppress HIV once ART is removed.
In the original RIO A phase (CROI 2025), 65% of bNAb recipients hadn't reached rebound criteria by week 20 — compared to just 8.8% in the placebo group. One participant from that phase has now maintained an undetectable viral load off ART for **four years** — the longest reported case of sustained drug-free HIV remission via bNAb therapy.
These are not cures in the absolute sense. Viral rebound eventually occurred in most participants, and researchers are clear that durable HIV remission will likely require combination strategies. But the direction of travel is unmistakable.
**What Comes Next**
A third phase of the RIO trial has been announced that will investigate whether intermittent periods of viral activity — paradoxically — might help re-sensitise the immune system to HIV, potentially generating fresh immune cells that improve long-term control.
The broader scientific community is watching closely. The 'vaccinal effect' hypothesis, if confirmed in larger trials, could transform HIV treatment strategy — shifting the goal from lifelong daily suppression toward periodic immune reinforcement that allows millions of people to live without constant medication.
For now, the RIO results represent the clearest evidence yet that the immune system can be taught, not just supported. And for 39 million people, that lesson matters enormously. 💊
*Sources: CROI 2026 (Conference on Retroviruses and Opportunistic Infections) · aidsmap · University of Oxford · riotrial.org · EATG · i-Base · Mass General Brigham*
