Background
The efficacy of flu shots varies from year to year and is not always optimal. In some seasons, traditional flu vaccines can reduce the risk of illness by as little as 20% to 30%. Messenger RNA (mRNA) technology is widely seen as a promising way to improve flu shot effectiveness, partly because it can be updated more quickly to match circulating strains.
Key Findings
New results published in the New England Journal of Medicine on May 6 found that Moderna's mRNA flu vaccine provided better protection than the standard flu shot in a Phase 3 clinical trial. The study involved more than 40,000 adults aged 50 and older during the 2024–2025 flu season across 301 sites in 11 countries.
- Efficacy improvement: About 2% of people in the mRNA vaccine group got sick, compared with 2.8% in the standard flu shot group — a relative risk reduction of approximately 27%.
- Safety profile: Side effects such as fatigue, headache and arm pain were more common in the mRNA group, but were mild and short-lived.
- Technology advantage: The mRNA platform allows for rapid updates to match seasonal circulating strains.
Regulatory Path and Outlook
Earlier this year, the U.S. Food and Drug Administration (FDA) refused to review Moderna's original flu vaccine submission. However, these strong new results could help bolster the vaccine's chances of approval. If approved, it would be the first mRNA-based flu vaccine authorized anywhere in the world.
Experts note that these results would make it difficult for the FDA to refuse again, and an mRNA flu shot could make a significant difference in flu prevention. Still, further evaluation of long-term safety and efficacy in different age groups is needed.