UK Phase I trial finds AI-designed coronavirus vaccine candidate safe and elicits cross-reactive immune responses

A Phase I trial in the U.K. found that an AI- and computationally designed coronavirus vaccine candidate was safe in 39 adults and triggered cross-reactive immune responses, offering an early signal for a broader vaccine strategy but not evidence that it prevents infection or disease.

The candidate, called pEVAC-PS, is designed to target conserved features shared across sarbecoviruses, the coronavirus subgroup that includes SARS-CoV-2, SARS-CoV-1 and related bat viruses. The idea is to train the immune system against viral parts that change less over time, rather than repeatedly updating vaccines to match individual variants.

Results from the first-in-human, dose-escalation trial were published in the Journal of Infection and made available online May 18. The vaccine was designed using computational and AI methods by DIOSynVax, a University of Cambridge spin-out. The trial was sponsored by University Hospital Southampton NHS Foundation Trust and run at National Institute for Health and Care Research clinical research facilities in Southampton and Cambridge.

The study enrolled 39 healthy adults ages 18 to 50. All had previously received two to three SARS-CoV-2 vaccine doses and did not have a recent confirmed coronavirus infection. Participants received two doses of the DNA vaccine 28 days apart. It was delivered into the skin using a needle-free micro-jet injector.

The trial’s main purpose was to test safety and reactogenicity, meaning the short-term side effects vaccines can cause. Researchers reported that pEVAC-PS was safe and well tolerated, with no serious adverse events or significant safety concerns in the 39 participants.

They also found measurable immune responses to conserved sarbecovirus epitopes — small pieces of virus targeted by the immune system — encoded by the vaccine. Press materials describing the study said those responses extended across SARS-CoV-2, SARS-CoV-1 and related bat sarbecoviruses.

But the immune findings came with important limits. The study authors said the signals were modest and difficult to interpret because participants already had high baseline immunity from prior COVID-19 vaccination and likely had varying exposure during Omicron waves. In other words, the trial suggests biological activity, but not how much additional protection the vaccine might provide.

That distinction matters because Phase I trials are built to answer narrow early questions: whether a candidate appears safe and whether it produces signs of an immune response. They do not show whether a vaccine protects people in the real world, how durable that protection might be, or whether it would work against future variants or newly emerging animal viruses.

A pan-sarbecovirus vaccine is sometimes described as a “universal” coronavirus vaccine, though in practice it means broader coverage within one viral family rather than protection against every coronavirus. pEVAC-PS is one of several efforts worldwide aiming to build vaccines that could hold up better against viral evolution and potential spillovers.

The paper’s lead and senior investigators include Alasdair P. S. Munro, Jonathan L. Heeney and Saul N. Faust, a University of Southampton researcher and the trial’s named chief investigator. The study began enrolling volunteers in December 2021, final enrollment was completed in September 2023, and the trial registry lists completion in September 2024.

Researchers said larger Phase II testing is planned to examine the breadth and durability of immune responses and to study the candidate in a broader population. In University of Cambridge press materials, Faust said that if such vaccines can be clinically advanced before the next outbreak, “millions of lives could be saved.” For now, though, the new data mark an early safety milestone, not proof of protection.