Overview
- In results published in the New England Journal of Medicine, Pfizer’s late-stage trial during the 2022–2023 season compared its mRNA vaccine with Fluzone in more than 18,000 adults ages 18 to 64 across the United States, South Africa, and the Philippines.
- The study recorded 57 flu cases in the mRNA group versus 87 with Fluzone, reflecting 34.5% relative efficacy, with most infections from influenza A strains H3N2 and H1N1 and protection also observed against B/Victoria and B/Yamagata.
- Side effects were more frequent with the mRNA shot, including fevers in 5.6% versus 1.7% with the traditional vaccine, though most reactions were mild to moderate and resolved within one to two days.
- No mRNA flu vaccine is approved yet, with Pfizer discussing a path to licensure with regulators and Moderna reporting about 27% relative efficacy in adults 50 and older and planning a filing by January 2026.
- Experts note mRNA flu products may differ in performance, and the platform’s rapid production timeline offers flexibility that traditional six-month egg-based manufacturing lacks.