FDA Advisory Panel Convenes Today to Weigh Moderna's mRNA-Based Flu Vaccine

The FDA's Vaccines and Related Biological Products Advisory Committee (VRBPAC) is meeting today, June 18, 2026, to evaluate the safety and effectiveness of Moderna's MFLUSIVA (Influenza Vaccine, mRNA), formerly known as mRNA-1010, for the prevention of seasonal influenza in adults 50 years of age and older.¹ The committee's recommendations are non-binding, but the FDA generally follows advisory panel guidance — and the outcome of today's vote is expected to shape the agency's final decision, which carries a PDUFA goal date of August 5, 2026.²

What does the clinical data show?

MFLUSIVA is a trivalent mRNA-based vaccine encoding hemagglutinin glycoproteins from WHO-recommended influenza strains. The BLA submission is backed by two phase 3 studies enrolling a total of 43,808 participants.³

The pivotal efficacy data, now published in the New England Journal of Medicine, come from the Phase 3 P304 trial — a randomized, double-blind, active-controlled study in adults aged 50 and older conducted across 11 countries. The trial compared mFLUSIVA against a licensed standard-dose seasonal influenza vaccine. Results showed a relative vaccine efficacy (rVE) of 26.6% (95% CI: 16.7%–35.4%) against RT-PCR–confirmed influenza-like illness, meeting prespecified criteria for both noninferiority and superiority over the comparator.⁴ Strain-specific rVE estimates were consistent across A/H1N1 (29.6%), A/H3N2 (22.2%), and B/Victoria lineages (29.1%).⁴

A second phase 3 study (P303 Part C) evaluated immunogenicity in adults 65 and older, comparing mFLUSIVA against a licensed high-dose influenza vaccine. Results suggested mFLUSIVA elicited superior immune responses relative to the high-dose comparator in this age group.^3,4

On safety, reactogenicity was higher with mFLUSIVA than with comparators — injection-site pain was reported in 65.8% of mFLUSIVA recipients versus 29.8% in the comparator group — though events were largely transient and mild to moderate in severity. No cases of myocarditis or pericarditis were reported, and serious adverse events were comparable across arms.⁴ The FDA's pre-meeting briefing documents noted no major efficacy deficiencies and confirmed that mFLUSIVA met all prespecified sequential success criteria, while flagging a limited safety follow-up window of six months and data drawn from a single flu season as areas warranting discussion.²

Why is this adcomm unusual?

The June 18 meeting comes at the end of an unusually contentious regulatory episode. In February 2026, the FDA's Center for Biologics Evaluation and Research (CBER) issued a rare refusal-to-file (RTF) letter, declining to initiate review of Moderna's original BLA. The RTF — signed by then-CBER director Vinay Prasad, MD, MPH — cited a single issue: Moderna's choice of a licensed standard-dose seasonal influenza vaccine as the comparator in its pivotal efficacy trial, arguing it did not reflect the "best-available standard of care" for older adults, who are preferentially recommended to receive high-dose or adjuvanted formulations.³

The decision was notable given that Moderna had conducted both pre-submission meetings and a separate phase 3 immunogenicity study comparing mFLUSIVA directly to a high-dose vaccine — data that were included in the submission. Moderna publicly disputed the FDA's rationale and posted the RTF letter on its website.³

Within days, the FDA reversed course following a Type A meeting with Moderna, accepting a revised application with an amended regulatory strategy: full approval for adults 50 to 64 years old, and accelerated approval for adults 65 and older, with a postmarketing requirement to conduct a confirmatory study in the older age group.² The adcomm today reflects the ongoing scrutiny of both the data and the comparator question in the context of a broader regulatory environment in which VRBPAC meetings have been convened less frequently under the current administration.²

The RTF episode did not occur in isolation. In August 2025, HHS announced the cancellation of more than 20 BARDA-funded mRNA vaccine development contracts totaling nearly $500 million — a decision that drew sharp criticism from researchers and former regulators.⁵ Among those who responded was Katalin Karikó, PhD, who shared the 2023 Nobel Prize in Physiology or Medicine for foundational work on mRNA technology. "Kennedy's decision to interfere with science is a huge mistake," Karikó said at the time. "National security of our country will suffer tremendously. Globally, vaccine research will progress in other corners of the world — in Europe, Asia, especially in China."⁵ While those comments were directed at the BARDA decision specifically, they reflect the broader institutional climate in which mFLUSIVA is now seeking US licensure.

What are the outstanding questions?

Beyond the comparator debate, the FDA has flagged several scientific uncertainties for the committee to consider. These include the single-season efficacy dataset, limited data in immunocompromised individuals and very frail older adults, and questions about whether immunogenicity results from P303 Part C can reliably predict clinical benefit against influenza B/Victoria subtypes due to limited confirmed cases in that strain.²

The stakes extend well beyond mFLUSIVA's individual approval. The vaccine would represent the first mRNA-based seasonal influenza product to receive FDA licensure. Regulatory filings are also under active review in the EU, Canada, and Australia. Should the committee vote favorably today and the FDA act by August 5, the vaccine could be available for the 2026–2027 flu season.²

References

1. Vaccines and Related Biological Products Advisory Committee June 18, 2026 Meeting Announcement. (2026 Jun 3). U.S. Food and Drug Administration. https://www.fda.gov/advisory-committees/advisory-committee-calendar/vaccines-and-related-biological-products-advisory-committee-june-18-2026-meeting-announcement
2. Garde D, Feuerstein A. (2026 Jun 17). Amenable FDA review bodes well for Moderna's mRNA flu shot ahead of adcomm grilling. Fierce Biotech. https://www.fiercebiotech.com/biotech/amenable-fda-briefing-docs-bode-well-modernas-mrna-flu-shot-ahead-adcomm-grilling
3. Moderna receives refusal-to-file letter from the U.S. Food and Drug Administration for its investigational seasonal influenza vaccine, mRNA-1010. (2026 Feb 10). BioSpace. https://www.biospace.com/press-releases/moderna-receives-refusal-to-file-letter-from-the-u-s-food-and-drug-administration-for-its-investigational-seasonal-influenza-vaccine-mrna-1010
4. Leroux-Roels I, Huang G, Ferguson M, et al; (2026 May 6). Efficacy and safety of an mRNA seasonal influenza vaccine in adults. N Engl J Med. https://www.nejm.org/doi/full/10.1056/NEJMoa2516491
5. Lavery P. (2025 Aug 11). mRNA vaccine development curtailed by HHS: key leaders respond. BioPharm International. https://www.biopharminternational.com/view/mrna-vaccine-development-curtailed-by-hhs-key-leaders-respond