Pfizer is under growing scrutiny from scientists, ethicists, and vaccine-skeptic groups after publishing Phase 3 trial results for its experimental mRNA flu vaccine in the New England Journal of Medicine that focus on adults under 65 while omitting detailed data for people 65 and older, the age group most at risk of severe influenza. Critics say the reporting gap raises questions about transparency and leaves policymakers and the public without crucial information on how the shot performs in seniors.
What the NEJM paper showed
The NEJM article reports results from a large Phase 3 trial of Pfizer’s quadrivalent modified mRNA (modRNA) flu vaccine in more than 18,000 adults, primarily ages 18 to 64, comparing it with a standard inactivated flu shot. In that population, the modRNA vaccine reduced symptomatic influenza A illness by about one‑third compared with the comparator and elicited stronger immune responses against H1N1 and H3N2 strains, though responses to influenza B were weaker. Side effects such as injection‑site reactions, fatigue, headache, and fever were more common with the mRNA shot, but serious adverse events were rare and similar between groups.
The missing data on older adults
Pfizer has previously acknowledged that the primary endpoints in adults 65 and older were not met in an earlier Phase 3 program of its first‑generation mRNA flu candidate, failing to show that the shot was at least “non‑inferior” to a licensed comparator in that age group. The company has also said it is running follow‑on trials of updated formulations, including studies specifically in seniors, and that data for adults 65 and older will be released later. However, the newly published NEJM paper centers on adults under 65 and does not present full efficacy and safety results for older participants, a choice that has become the focus of criticism.
Why experts are concerned
Influenza hospitalizations and deaths are concentrated in people 65 and older, making the performance of any next‑generation flu vaccine in seniors a central public‑health question. Independent experts quoted in scientific outlets have welcomed the stronger protection seen in younger adults but stressed that the trial does not yet prove the vaccine is safe and effective in the very populations that need it most. Some commentators argue that publishing high‑profile Phase 3 results without parallel, granular disclosure of the senior data—especially after earlier non‑inferiority failures in that age group—risks eroding public trust and fueling suspicion around mRNA technologies.
Pfizer’s response and next steps
Pfizer has framed the NEJM publication as an important milestone demonstrating that an mRNA flu vaccine can outperform a standard-dose seasonal shot in adults under 65, while characterizing the program in older adults as “ongoing” and subject to further optimization of strain composition and dosing. The company says it plans to refine its formulations to improve responses to influenza B and in older populations, and will discuss next steps with regulators once more data are available. Regulators and advisory groups will ultimately need the full dataset, including seniors, before deciding whether and how an mRNA flu vaccine should be used alongside or in place of existing high‑dose and adjuvanted flu shots currently recommended for older adults.
Key issues at stake
Public‑health advocates say the episode highlights a broader debate over how much interim or age‑restricted data should appear in top journals when companies are still working to fix shortfalls in high‑risk groups. Transparency advocates are calling for Pfizer and other manufacturers to publish age‑stratified efficacy and safety outcomes for seniors as soon as practicable, even if results are mixed, to ensure clinicians and the public can make informed decisions about emerging mRNA flu technologies. Meanwhile, enthusiasm over the promise of mRNA‑based flu shots is tempered by reminders from experts that more research is needed, especially in the elderly, before these vaccines can be seen as ready to replace entrenched seasonal flu products.
