An FDA advisory panel voted unanimously on Thursday that Moderna’s mRNA seasonal influenza vaccine, mFLUSIVA, should be approved for adults aged 50 and older, a decisive endorsement that moves the world’s second mRNA vaccine platform (after COVID-19 shots) closer to market.
The Vaccines and Related Biological Products Advisory Committee (VRBPAC) held two votes, each returning 9-0: one for adults aged 50-64 via the traditional approval pathway, and a second for adults 65 and older via accelerated approval, subject to post-marketing confirmatory study commitments. The FDA is not bound by the vote but typically follows its advisory committees’ recommendations.
The PDUFA goal date for an FDA decision is August 5, 2026, with potential availability for the 2026-2027 flu season if approved.
Moderna’s Phase 3 program comprised two studies with a total of 43,808 participants across 301 sites in 11 countries.
The pivotal P304 trial (the “Fluent” study) enrolled 40,805 adults aged 50 and older in a randomized, double-blind, active-controlled design comparing mFLUSIVA against standard-dose seasonal flu vaccine. Results, published in the New England Journal of Medicine, showed:
- A relative vaccine efficacy (rVE) of 26.6% (95% CI: 16.7-35.4) against influenza-like illness compared to standard-dose vaccine
- A 47.9% rVE against healthcare utilization endpoints (doctor visits, hospitalizations)
- Strain-specific rVE of 29.6% against A/H1N1, 22.2% against A/H3N2, and 29.1% against B/Victoria
- All prespecified sequential noninferiority and superiority criteria met
For the older cohort, a second study (P303 Part C, n=3,003) compared mFLUSIVA head-to-head against Fluzone High-Dose, the current standard for adults 65+. Moderna’s vaccine demonstrated superior immune responses, higher antibody GMTs and seroconversion rates, across all four influenza strains.
The controversy
The path to Thursday’s vote was anything but smooth. In February 2026, the FDA’s Center for Biologics Evaluation and Research (CBER), then led by Dr. Vinay Prasad, issued a rare Refusal-to-File (RTF) letter rejecting Moderna’s initial Biologics License Application submission. The stated reason: Moderna’s Phase 3 trial used a standard-dose flu vaccine as the comparator, whereas adults 65 and older are recommended to receive high-dose or adjuvanted formulations. Prasad argued this did not represent the “best available standard of care.”
Moderna publicly disputed the decision, posting the RTF letter on its website and noting that FDA staff had approved the trial design before it began. After a Type A meeting days later, the FDA reversed course and accepted a revised application with a split strategy, full approval for adults 50-64, accelerated approval for 65+.
The episode occurred amid a broader period of turmoil at the agency, as heightened vaccine scrutiny from HHS Secretary Robert F. Kennedy Jr. coincided with the departures of both FDA Commissioner Marty Makary and CBER director Prasad.
Safety profile
The safety data showed a predictable pattern for mRNA vaccines. Injection-site pain was reported in 65.8% of mFLUSIVA recipients versus 29.8% for standard-dose comparator. Fatigue (45.1% vs 20.3%), headache (37.8% vs 18.0%), and myalgia (35.4% vs 11.6%) were also higher. Most events were mild to moderate and transient. No cases of myocarditis or pericarditis were reported. Serious adverse events were comparable between groups (2.2% mRNA vs 1.9% comparator).
Panel member Adam Berger, Ph.D., said the evidence “largely supports safety and effectiveness” while noting limitations including single-season data and limited subgroup detail.
Remaining questions
FDA scientists flagged several data gaps for the panel: the study covers only a single flu season, providing no information on year-to-year performance against different circulating strains. Confidence intervals for the B/Victoria strain crossed zero due to low case counts. There are no data in immunocompromised or very frail older adults, the populations at highest risk from influenza, and no co-administration data with COVID-19, RSV, or pneumococcal vaccines.
Post-marketing requirements would include a confirmatory Phase 4 study for the 65+ accelerated approval pathway, which Moderna has committed to conducting.
What’s next
Beyond the August 5 PDUFA date, Moderna’s mRNA flu vaccine is under regulatory review in the European Union, Canada, and Australia. Additional country submissions are planned through 2026. If approved, mFLUSIVA would be the first mRNA-based seasonal influenza vaccine to reach the market, competing with traditional egg-based and cell-culture flu shots that have dominated for decades.
Source: STAT News, “FDA advisory panel endorses Moderna mRNA flu vaccine that was subject of controversy” by Helen Branswell (June 18, 2026). https://www.statnews.com/2026/06/18/fda-mrna-flu-vaccine-vrbpac-advisers-endorse-moderna-shots/