British Medical Journal
Published April 22, 2026
Bird Flu: mRNA Vaccine Trial Begins in United Kingdom
A trial of a potential mRNA vaccine against avian flu is starting in the UK as part of the country’s preparedness for a potential pandemic.
Avian flu, an infectious disease caused by the influenza A virus, is found in wild birds and poultry in much of the world. It has also spread to various mammals, including dairy cattle in the US. Some subtypes such as A(H5N1) or A(H7N9) have been associated with human disease, usually in people who have been directly exposed to infected birds or animals. However, experts warn that although the risk to humans is currently low, the virus could adapt and become more transmissible, leading to a future pandemic. There have been around 1,000 confirmed human Bird Flu cases reported to the World Health Organization since 2003 and nearly half of those proved fatal. More recently, a strain circulating in the United States caused milder symptoms with eye inflammation being the primary symptoms
The phase 3 trial will assess the safety and immune response of Moderna’s investigational vaccine, mRNA-1018, against that targets the H5N1 flu strain which has caused devastating infections in bird populations worldwide and has spread to some mammals. The vaccine uses the same mRNA technology used in current Covid jabs, with scientists saying this enables the vaccine to be created quickly and at scale, in the event of a pandemic. The large-scale trial will involve 4,000 volunteers with three-quarters recruited at 26 sites in England and Scotland, and the rest in the United States. There have been 116 confirmed human cases around the world since 2024, almost all linked to close contact with infected animals. The study will examine whether the vaccine is safe and can generate a strong immune response. If so, it could then be licensed for use if needed.
The traditional method of creating flu vaccines involves growing the virus in eggs - but this can be a problem when there are virulent avian flu strains which can kill the eggs used during manufacturing. During the Covid pandemic, mRNA vaccines were shown to be highly effective at preventing serious illness, and could be produced and altered rapidly, as strains evolved. Flu pandemics are inevitable, even if the timing of the next global outbreak is uncertain. The flu virus is constantly evolving, which is why a new flu jab is needed every year.
A flu pandemic occurs when the strain shifts, rather than drifts, sufficiently that humans do not have any natural immunity to it. The last one in 2009, called swine flu, was comparatively mild. But the pandemic of Spanish flu after the First World War killed around 50 million people worldwide. It is impossible to know if H5N1 will be the strain that causes the next flu pandemic.