The FDA's vaccine advisers (VRBPAC) vote Thursday on Moderna's mFlusiva, the first mRNA flu vaccine to reach a US advisory review, and the briefing documents still leave the standard dose comparator question to the panel, a year after a 2026 FDA refusal to file (a procedural…
The mRNA vaccine platform earned its credibility in COVID-19. On Thursday, June 18, it faces a much smaller and more routine test: whether Moderna's mRNA-based flu shot can win over the FDA's vaccine advisory panel, in what would be the first time an mRNA flu vaccine has reached a US advisory vote (Fierce Biotech, June 16, 2026).
The candidate, called mFlusiva, is a messenger-RNA vaccine that encodes a hemagglutinin protein from circulating flu strains, the same basic approach Moderna's COVID shots used. What makes Thursday unusual is not the science but the regulatory moment: mRNA proved itself in a pandemic, and the annual flu market is the first place it would have to prove itself outside one.
The advisory committee in question is the FDA's Vaccines and Related Biological Products Advisory Committee, a standing panel of outside experts whose votes the FDA almost always follows but is not legally required to. The panel will weigh two questions, one for adults 50 to 64 and one for adults 65 and older, with the older group being the harder one.
Earlier in 2026, the FDA sent Moderna a refusal-to-file letter, a procedural rejection that means the agency would not open the application for substantive review. The trigger was a methodological objection to the control arm in Moderna's Phase 3 trial, specifically the choice of a standard-dose seasonal flu shot as the comparator rather than a high-dose or adjuvanted version typically used in older adults. Vinay Prasad, who led the FDA's Center for Biologics Evaluation and Research at the time, signed the letter. The issue became the first public, named regulatory objection to the program.
On Tuesday, the FDA released the briefing documents that will frame Thursday's discussion. According to Fierce Biotech's reading of those documents, the tone is now more measured, and the agency describes mFlusiva's effectiveness as hitting its pre-specified goals. But the briefing documents do not retire the control-arm question. Instead, they hand it back to the panel: VRBPAC is being asked to weigh whether the standard-dose comparator is the right benchmark in the older-adult arm, the same issue that triggered the refusal-to-file letter.
That sequence is the actual story. The FDA's own prior objection is being re-aired in public, on the same candidate, with the same committee, two days after the briefing documents softened the agency's language. The platform is being asked to clear a procedural hurdle the agency had previously used to keep it out the door, in front of a non-binding vote that will still shape the eventual approval decision.
The vote questions frame the older-adult arm as the harder one. If the panel votes against the standard-dose comparator, the FDA can still approve mFlusiva, but the labeling and indication would likely be narrower. If the panel votes in favor, the application returns to its original trajectory. Either result is non-binding, and the agency can, and sometimes does, reach a different conclusion.
What to watch after Thursday's vote: whether the FDA includes both age groups in any eventual approval language, or narrows the indication to adults under 65; whether Moderna has to run a confirmatory trial with a different comparator in older adults; and whether the mRNA platform, having cleared COVID, gets its first non-pandemic US indication at all.