SOUTHAMPTON — The first volunteers in the United Kingdom have been immunised with Moderna's H5N1 vaccine designed to protect against a potential bird flu pandemic, with early injections administered at a clinic in Southampton. The trial will enroll 4,000 participants, with three-quarters recruited across 26 sites in England and Scotland and the remainder in the United States.

The study will examine whether the mRNA-based vaccine is safe and can generate a strong immune response. If the vaccine proves safe and immunogenic, it could be licensed for use. Recruitment is targeting people who work in the poultry industry and people over the age of 65.

Clare Howard, a Hampshire resident who has kept chickens for years, was among the first volunteers to receive the vaccine at the Southampton clinic. "It was quite easy and it could be something that ultimately proves incredibly important," Howard said.

Dr Rebecca Clark, the trial's national coordinating investigator based at Layton Medical Centre in Blackpool, addressed the rationale for the study. "Although it does not yet move easily between humans, we have to treat human-to-human transmission as a real possibility," she said. "This trial is our proactive attempt to shield against that possibility, and any future pandemic that could emerge from it."

H5N1 has caused infections in bird populations worldwide and has spread to some mammals. The UK Health Protection Agency says the threat from H5N1 to humans is currently low, and almost all human cases are linked to close contact with infected animals. There have been 116 confirmed human H5N1 cases around the world since 2024. Since 2003, the World Health Organization has reported around 1,000 confirmed human H5N1 cases, nearly half of them fatal. A strain circulating in the United States recently caused milder symptoms, primarily eye inflammation.

If needed, the vaccine would be manufactured at Moderna's new plant at Harwell in Oxfordshire, which currently produces Covid vaccines for the UK. The site can produce 100 million doses per year, with capacity that could be increased to 250 million doses per year in the event of a pandemic. Traditional flu vaccine production involves growing the virus in eggs, and virulent avian flu strains can kill the eggs used during manufacturing. During the Covid pandemic, mRNA vaccines were shown to be effective at preventing serious illness and could be produced and altered rapidly as strains evolved.

Professor Lucy Chappell, chief scientific adviser at the Department of Health and Social Care and CEO of the National Institute for Health and Care Research, said the trial was "bolstering our pandemic resilience." CEPI provided £40 million of funding for the trial. As part of the deal, Moderna agreed to guarantee fast and affordable vaccine supply to low- and middle-income countries in any future pandemic, a measure CEPI said would mitigate against the vaccine nationalism seen during the Covid pandemic.

A 2006 trial of an H5N1 vaccine in Oxford found the jab to be safe but not very effective. The flu virus is constantly evolving, which is why a new flu vaccine is needed every year, and a flu pandemic occurs when a strain shifts sufficiently that humans lack any natural immunity to it. The last flu pandemic was in 2009 and was called swine flu.