CAMBRIDGE, Mass. — Moderna on Wednesday reported that its mRNA-based H5N1 bird flu vaccine demonstrated 82.7% efficacy against symptomatic infection in an interim analysis of its ongoing Phase 3 trial, a result the company called a critical milestone in pandemic preparedness.
The trial, which began enrollment in early April, has dosed roughly 4,000 healthy adults across 38 sites in the United States and United Kingdom. The interim analysis, conducted by an independent Data Safety Monitoring Board, evaluated the first 142 confirmed cases of H5N1 infection among participants, with 17 cases occurring in the vaccine arm and 125 in the placebo arm. The vaccine, designated mRNA-1018, also showed a favorable safety profile, with adverse events largely limited to transient injection-site pain, fatigue and low-grade fever, and no excess rate of myocarditis or pericarditis observed at either the 25- or 50-microgram dose levels.
"These results validate the platform's ability to respond quickly and effectively to emerging zoonotic threats," said Dr. Stephen Hoge, President of Moderna, on a call with analysts Wednesday morning. "An efficacy figure above 80% against H5N1 gives public health authorities a powerful new tool should this virus continue to evolve toward broader human transmission."
The announcement comes amid sustained concern over H5N1 outbreaks in U.S. dairy cattle, which have now spread to 19 states, and sporadic human cases reported since 2024. Dr. Peter Marks, director of the FDA's Center for Biologics Evaluation and Research, said in a briefing Wednesday afternoon that the agency had reviewed the interim data and considered the benefit-risk profile "highly favorable" based on the evidence submitted to date. Dr. Nicole Lurie, Executive Director for Preparedness and Response at the Coalition for Epidemic Preparedness Innovations (CEPI), called the data "the most encouraging news we've had on H5N1 countermeasures in years."
Moderna confirmed it has begun rolling submissions to the U.S. Food and Drug Administration and the U.K. Medicines and Healthcare products Regulatory Agency, and expects to file for full Biologics License Application by the third quarter of 2026. The Biomedical Advanced Research and Development Authority (BARDA), which has invested $176 million in the program since 2023, said it would exercise contract options to secure an initial 50 million doses for the U.S. Strategic National Stockpile. The Department of Health and Human Services said in a statement that the new doses would supplement existing egg- and cell-based H5N1 vaccines from Sanofi and CSL Seqirus already held in the stockpile.
Shares of Moderna rose 11.4% in pre-market trading following the announcement. The company said it expects to complete the full Phase 3 readout by early 2027, with continued follow-up to assess durability of protection.