Moderna Launches Phase 3 Bird Flu Vaccine Trial Across US and UK

A Landmark Moment for mRNA Pandemic Preparedness

Moderna has begun dosing participants in a Phase 3 clinical trial of mRNA-1018, its mRNA-based H5 pandemic influenza vaccine candidate. This marks the first time an mRNA vaccine aimed at pandemic flu has entered late-stage testing, a milestone many public health experts have been anticipating for years.

The randomised, observer-blind, placebo-controlled study will enrol approximately 4,000 healthy adults aged 18 and over across the United States and the United Kingdom. Roughly 75% of participants will be recruited at UK sites, with priority given to adults over 65 and poultry farmers, who face elevated exposure risk from avian influenza.

Funding Turbulence and CEPI's Rescue

The trial is backed by up to $54.3 million from the Coalition for Epidemic Preparedness Innovations, which announced its investment in December 2025. CEPI's commitment came after the Trump administration cancelled more than $700 million in federal contracts that had previously supported Moderna's pandemic influenza work. The Department of Health and Human Services terminated the funding in May 2025, arguing that continued investment was not scientifically or ethically justifiable and describing mRNA technology as undertested.

As part of the new arrangement, Moderna has committed to allocating 20% of its manufacturing capacity for mRNA-1018 to supply low- and middle-income countries at affordable prices in a pandemic scenario.

Strong Early Data

The Phase 3 study builds on encouraging Phase 1/2 results from roughly 300 healthy adults, in which nearly 98% of participants achieved protective antibody levels by day 43 after two doses, a 44.5-fold increase from baseline. Moderna plans to leverage data from its seasonal influenza vaccine trials to support a potential approval pathway for the H5 candidate.

The UK arm of the study is supported by the National Institute for Health and Care Research and the UK Health Security Agency. Estimated primary completion is January 2027.

Why It Matters

H5N1 continues to spread among birds and livestock, with a growing number of human infections, primarily among agricultural workers. If mRNA-1018 succeeds, it could offer a dramatically faster manufacturing alternative to traditional egg-based flu vaccines, a capability widely considered essential for rapid pandemic response.