A major new clinical trial for an mRNA bird flu vaccine is set to begin in Britain in the coming weeks, it was announced on Wednesday.

The trial will recruit 3,000 participants from across the country to assess how effectively the jab protects against the virus which scientists fear could trigger the next pandemic.

The study is being led by Moderna in partnership with the UK Health Security Agency (UKHSA), the government body responsible for managing threats to public health in Britain.

Originating in birds, the H5N1 virus has spread rapidly through animal populations in recent years, decimating millions of farmed birds worldwide and infecting a range of mammals, including dairy cattle, cats, bears and foxes.

Since 2024, at least 114 human cases have been recorded, all linked to close contact with infected animals.

The new vaccine uses messenger RNA technology – the same platform that enabled the rapid development of several Covid-19 vaccines.

It allows for faster production than traditional methods and is considered particularly suited to responding quickly during large-scale outbreaks.

“By advancing research on an investigational mRNA vaccine against pandemic influenza and supporting rapid clinical trial delivery in the UK, we are helping build the evidence, experience and readiness that can inform future responses to emerging public health threats,” said Darius Hughes, UK General Manager at Moderna.

The study will run across 26 clinics in England and Scotland in cities including London, Glasgow, Blackpool, and Newcastle. 

At least half of the recruits will be over the age of 65, the organisers of the trial said. 

They are the most vulnerable to the flu and would most likely be given first-priority should H5N1 start to spread human to human. 

Farmers and those who work closely with poultry – and therefore are most at risk – will also be encouraged to come forward for the trial, the organisers said. 

In 2024, health authorities signed an agreement with the vaccine manufacturer CSL Sequirus to secure five million doses of an H5N1 jab should the virus break out in the UK. 

However, the vaccines are produced using egg-based technology – meaning they are grown and cultured inside of chicken eggs, a process used for flu jabs over 70 years – which takes several months and would be difficult to accelerate in an emergency. 

“One of the key lessons from the Covid was that speed of response is critical for saving lives.  Doing a large scale human vaccine trial for H5N1 now, allows for a more rapid scale up of response if the virus spreads in the future,” Prof John Tregoning, Professor of Vaccine Immunology, Imperial College London.

Should the virus acquire the ability to spread easily between people, experts warn it could pose a serious pandemic threat due to low population immunity and a historically high fatality rate. Of roughly 1,000 human infections recorded since 1990, nearly half have been fatal.

Several major pandemics have been linked to animal influenza strains, including the 2009 swine flu outbreak and the 1918 influenza pandemic, which killed an estimated 50 million people worldwide.

“We don’t know when the next pandemic will occur or what will cause it, but we do know that influenza remains the most likely candidate,” said Richard Pebody, Director of Epidemic and Emerging Infections at UKHSA, speaking at a press conference.

Protect yourself and your family by learning more about Global Health Security