A major global vaccine trial has officially begun as scientists race to prepare for what they warn could be the next pandemic threat—bird flu in humans.
Researchers in the UK and US have launched a large-scale clinical trial of an mRNA-based H5N1 bird flu vaccine, designed to test whether humans can be protected before the virus gains the ability to spread efficiently between people.
At the center of this effort is a stark scientific warning: while H5N1 currently spreads mainly among birds and animals, experts say human-to-human transmission is now a “real possibility” that cannot be ignored.
A vaccine built on Covid-era technology
The experimental vaccine, mRNA-1018, developed by Moderna, uses the same mRNA platform that powered Covid-19 vaccines.
Instead of using weakened virus material, the vaccine instructs the body to produce harmless viral proteins—training the immune system to recognize and fight H5N1 quickly if exposed.
Early studies suggest the jab is well tolerated and capable of producing a strong immune response within days, according to Moderna’s clinical development team.
Related story: WHO urges enhanced Bird Flu surveillance amid rising global cases
4,000 participants in major global trial
The Phase 3 trial will enroll around 4,000 participants across the UK and US, including:
- Approximately 3,000 volunteers in the UK
- Half of them aged 65 and above
- Recruitment across 26 clinical sites including London, Glasgow, Newcastle, and Blackpool
- Priority inclusion of poultry workers and high-risk animal handlers
The trial is backed by the UK Health Security Agency (UKHSA) and the National Institute for Health and Care Research (NIHR), and will run for about seven months, with participants receiving two doses spaced three weeks apart.
Why scientists are worried about H5N1
The H5N1 avian influenza virus has spread widely in recent years, affecting:
- Poultry and wild birds
- Dairy cattle in the US
- Mammals including mink, foxes, and even marine animals
Since 2024, at least 114–116 human cases globally have been recorded, almost all linked to direct contact with infected animals.
While human cases remain rare, the virus carries a high fatality rate in reported infections, making it a serious concern for pandemic preparedness experts.
“We must prepare before it spreads”
Dr Rebecca Clark, national co-ordinating investigator for the trial, said the goal is proactive protection:
“We have to treat human-to-human transmission as a real possibility. This trial is our attempt to prepare for that scenario and any future pandemic threat.”
Similarly, UKHSA experts stressed that although current human risk remains low, influenza remains one of the most likely causes of future pandemics.
Why speed matters in vaccine development
Experts highlight a key advantage of mRNA technology: speed and adaptability.
Unlike traditional egg-based flu vaccines, which can take months to produce, mRNA vaccines can be developed and scaled rapidly—an essential factor in any future outbreak response.
Professor John Tregoning of Imperial College London noted that early large-scale trials like this help ensure faster deployment if a pandemic emerges.
A global warning shaped by history
The concern is not theoretical.
Influenza has triggered some of the deadliest pandemics in history, including:
- The 1918 Spanish flu (estimated 50 million deaths)
- The 2009 swine flu pandemic
Scientists caution that if H5N1 gains efficient human transmission ability, global populations would be highly vulnerable due to low immunity levels.
The bigger picture
While officials stress the current risk to the public is still low, the message from researchers is clear:
Preparation must begin before a pandemic begins—not after.
This trial marks one of the most significant steps yet in global readiness for emerging influenza threats.
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