An investigational seasonal flu vaccine from Moderna is under FDA review. The candidate tries to close the gap in years when the egg based shots pick the wrong strains.
Moderna's mRNA flu vaccine is now in front of FDA reviewers, and the supporting immunology work tries to answer a question tens of millions of Americans ask every fall: why does the seasonal flu shot sometimes barely work?
The mismatch problem is the public-health stakes. Today's flu vaccines are grown in chicken eggs, and the World Health Organization and regulators have to pick the strains they expect to dominate roughly six months before the season starts. When that guess is right, vaccine efficacy can run around 60%. When it is wrong, that figure can collapse to roughly 19% (Genetic Engineering and Biotechnology News summary of the development).
The candidate under review takes a different approach. Instead of delivering an inactivated virus, the mRNA platform teaches the body to make its own target protein and can be re-coded much faster when the circulating strains drift. The immunology package — a study published in Nature Immunology (s41590-026-02569-5) — describes a broader B cell response, meaning the immune system trains against more parts of the virus than just the head of the hemagglutinin protein, which is the section today's shots target.
The study followed 75 adults ages 20–50 over the 2022–2024 Northern Hemisphere flu seasons, with 38 receiving the investigational mRNA vaccine (mRNA-1010) and 37 receiving Fluarix. Both targeted the same WHO-recommended strains. Among a subset who underwent lymph node sampling, five of 13 mRNA-1010 recipients showed persistent germinal center responses at 26 weeks, compared with zero of 15 Fluarix recipients. Antibodies from mRNA vaccine recipients also recognized a wider range of flu strains, including those spanning multiple decades of viral evolution.
That broader training is what proponents say could close the gap in bad-match years. It is not yet the same thing as proven real-world protection across multiple flu seasons, and the FDA review is not approval. An advisory committee may be required, and the timeline is uncertain.
The track record here is mixed. Moderna's own mRNA-1010 Phase 3 readout produced results that did not meet the primary endpoint in one readout, and a separate Sanofi-Translate Bio mRNA flu partnership was also discontinued. The mRNA platform carries well-known concerns that any seasonal program will have to address: cost per dose, cold-chain storage, and a rare myocarditis signal that surfaced with the COVID-19 mRNA vaccines.
For now, the candidate remains investigational. It is not approved, not available to the public, and the FDA's decision is the next real test of whether a "broader" immune response on paper translates into better odds the next time the seasonal strain guess goes wrong.