Moderna has begun a large-scale Phase III trial of its mRNA-based H5N1 bird flu vaccine in the United Kingdom and United States after federal funding was withdrawn by the Department of Health and Human Services.
The trial, which will enroll 4,000 participants — 3,000 in the UK and 1,000 in the US — focuses on measuring immune response rather than direct efficacy, as sustained human-to-human transmission of the virus has not yet been observed. Participants prioritized include adults over 65 and individuals with occupational exposure to poultry or dairy cattle, groups identified as most vulnerable to infection.
This development follows the cancellation of hundreds of millions of dollars in previously committed HHS funding for mRNA vaccine development under Secretary Robert F. Kennedy Jr.’s leadership. The Washington Post reported that the terminated grants had been earmarked to advance pandemic preparedness efforts, including work on avian influenza threats.
With U.S. Government support retracted, the Coalition for Epidemic Preparedness Innovations (CEPI) assumed financial responsibility for the trial. CEPI, a global partnership backed by more than 30 countries and organizations, has a history of stepping in when national funding for epidemic countermeasures stalls, as seen during early COVID-19 vaccine development.
The vaccine candidate, designated mRNA-1018, has already cleared Phase I and II safety reviews with no significant adverse events reported. Earlier data indicate a robust immune response, giving researchers confidence as they move into larger-scale testing. Unlike conventional egg-based flu vaccines, which dominate current national stockpiles, mRNA platforms allow for rapid redesign and scalable production — critical advantages if the H5N1 strain evolves to spread more easily among people.
Although more than 100 human cases of H5N1 have been recorded since 2024, primarily linked to direct animal contact, there remains no evidence of sustained community transmission. Experts caution that the virus’s continued circulation in wild birds, poultry, and now dairy cattle increases opportunities for mutation. Richard Pebody of the UK Health Security Agency emphasized that influenza pandemics remain the most probable biological threat, underscoring the importance of having countermeasures ready before outbreaks escalate.
The UK maintains a stockpile of approximately 5 million doses of traditional H5N1 vaccine, but officials acknowledge the limitations of egg-based manufacturing in responding to a fast-moving pandemic scenario. Moderna’s approach, by contrast, could allow for updated doses to be designed and produced within weeks of detecting significant genetic shifts in the virus.
Hiwot Hiruy of Moderna noted that even as the timing and severity of any future pandemic cannot be predicted, the precedent of delayed vaccine deployment during the early COVID-19 period — when millions died before shots became widely available — makes proactive investment in platform technologies like mRNA a matter of strategic necessity.
How the trial design accounts for the absence of widespread human infection
Because H5N1 has not demonstrated efficient person-to-person spread, researchers cannot test whether the vaccine prevents illness in real-world conditions. Instead, the study will assess neutralizing antibody levels and T-cell responses in volunteers, comparing them to benchmarks established from earlier phases. A strong immunogenic profile would support regulatory advancement under accelerated pathways, should transmission patterns change.
Why CEPI’s involvement signals a broader shift in pandemic funding
The withdrawal of federal backing for an mRNA influenza vaccine trial highlights growing reliance on multilateral institutions to fill gaps left by national policy shifts. CEPI’s role mirrors its function during the 2020–2021 period, when it helped finance multiple COVID-19 vaccine candidates amid uncertainty over domestic funding commitments. This model may develop into more common if geopolitical or administrative fluctuations continue to affect long-term biodefense planning.
What is the current risk of H5N1 bird flu to the general public?
Based on available data, the risk to the general public remains low. All confirmed human cases since 2024 have involved direct exposure to infected animals, with no documented instances of sustained human-to-human transmission. Health agencies continue to monitor viral evolution in animal populations closely.
How does an mRNA vaccine differ from existing bird flu shots in stockpiles?
Existing stockpiled vaccines rely on egg-based technology, which requires months to produce and cannot be easily modified if the virus mutates significantly. MRNA vaccines can be redesigned quickly and manufactured at scale using synthetic processes, offering greater flexibility in responding to evolving strains.
