It has been more than three years since Moderna's mRNA technology proved it could protect against a respiratory virus in the real world. Today, that platform faces a new and historic test: the first-ever FDA advisory committee vote on an mRNA-based seasonal influenza vaccine.
The FDA's Vaccines and Related Biological Products Advisory Committee (VRBPAC) convened June 18, 2026, to assess the benefit-risk profile of MFLUSIVA (mRNA-1010), Moderna's investigational trivalent mRNA seasonal influenza vaccine, with the FDA's formal decision date set for August 5, 2026. The pre-meeting briefing documents released June 16 showed no "major deficiencies," triggering a 9% stock surge and setting up what may be a landmark moment in vaccine history.
What MFLUSIVA Is — and What the Phase 3 Trial Showed
MFLUSIVA (formerly mRNA-1010) is an mRNA-based trivalent influenza vaccine containing antigens against four influenza strains: H1N1, H3N2, B/Yamagata (included for formulation stability), and B/Victoria. It is manufactured by Moderna TX Inc. and is being reviewed under Biologics License Application STN 125869/0 for the prevention of influenza disease caused by influenza virus subtypes A and type B in persons 50 years of age and older.
The pivotal Phase 3 trial, mRNA-1010-P304, enrolled 40,805 adults across 301 sites in 11 countries in North America, Europe, and East Asia. The primary endpoint results, as detailed in FDA briefing documents covered by Pharmaceutical Executive:
- Relative Vaccine Efficacy (RVE) of 26.6% against RT-PCR-confirmed influenza-like illness compared to a standard-dose comparator vaccine (95% CI: 16.7–35.4)
- RVE rising to 47.9% when measured against higher-level healthcare outcomes — emergency room visits, hospitalizations, and urgent care use
- FDA staff concluded the study "met all prespecified sequential success criteria"
- No major safety issues identified; no imbalances in adverse events or deaths between treatment and placebo groups
A separate immunogenicity study (3,003 participants aged 65 and older) compared MFLUSIVA against Fluzone High-Dose — the CDC-preferred influenza vaccine for older adults. MFLUSIVA met prespecified noninferiority and superiority criteria on antibody geometric mean titers and seroconversion rates across all four vaccine-matched strains at Day 29, with immune responses remaining elevated at the six-month follow-up.
| MFLUSIVA Phase 3 Trial and FDA Review Key Data | Detail |
| Vaccine name | MFLUSIVA (mRNA-1010), Moderna TX Inc. |
| BLA number | STN 125869/0 |
| VRBPAC meeting date | June 18, 2026 |
| PDUFA (FDA decision) date | August 5, 2026 |
| Phase 3 trial (P304) enrollment | 40,805 adults; 301 sites; 11 countries |
| RVE vs. standard-dose comparator (ILI primary endpoint) | 26.6% (95% CI: 16.7–35.4) |
| RVE vs. standard-dose (healthcare outcomes) | 47.9% |
| FDA finding | "No major deficiencies"; "met all prespecified sequential success criteria" |
| Safety | No major concerns; no adverse event imbalances |
| Ages 50–64 approval pathway | Traditional approval (based on clinical efficacy data) |
| Ages 65+ approval pathway | Accelerated approval (based on immunogenicity; Phase IV trial required) |
| Immunogenicity vs. Fluzone High-Dose (65+) | Superior across all 4 strains at Day 29 and 6-month follow-up |
| mRNA flu vaccine previously approved in U.S. | None |
The Two-Question Vote — and the Accelerated Approval Framework
The VRBPAC panel was asked to vote on two distinct questions, one for each age group:
Question 1 — Adults 50–64 (Traditional Approval): Does the benefit-risk profile of MFLUSIVA support traditional approval for the prevention of influenza in adults ages 50 through 64? For this group, Moderna has strong clinical efficacy data from Study P304 showing meaningful relative vaccine efficacy over standard-dose vaccine — the standard comparator for this age group.
Question 2 — Adults 65+ (Accelerated Approval): Does the benefit-risk profile of MFLUSIVA support accelerated approval for the prevention of influenza in adults ages 65 and older, with a required post-marketing Phase IV confirmatory trial? For this group, the regulatory strategy is different — because the CDC preferentially recommends high-dose, recombinant, or adjuvanted flu vaccines for adults 65 and older (rather than standard-dose), direct head-to-head clinical efficacy against the high-dose comparator has not been fully established. Moderna is instead seeking accelerated approval based on the immunogenicity superiority data, with a commitment to conduct a Phase IV confirmatory trial to establish clinical benefit in this population.
This bifurcated regulatory strategy was directly shaped by a turbulent regulatory backstory. In February 2026, the FDA issued a Refusal to File (RTF) letter to Moderna, with the FDA's then–Center for Biologics Evaluation and Research director Vinay Prasad citing concerns that Moderna had not used a high-dose vaccine as the comparator for the older adult population — which is standard of care. Days later, the FDA reversed course, allowing the revised application to proceed after Moderna modified its regulatory strategy to differentiate by age group. The August 5 PDUFA date and June 18 advisory committee meeting followed.
What the FDA Flagged for the Panel's Consideration
Even as the FDA's briefing documents described no major deficiencies, agency scientists flagged four specific areas of uncertainty for the advisory committee to weigh:
1. Single flu season of data. All efficacy data comes from one influenza season — leaving open how MFLUSIVA would perform against the different circulating strains of subsequent years, which change annually and can vary significantly in severity and composition.
2. Influenza B/Victoria uncertainty. The confidence interval for MFLUSIVA's efficacy against the B/Victoria strain crossed zero due to low case accrual for that strain, leaving its protective effect against influenza B specifically uncertain.
3. Immunocompromised and very frail older adults not studied. These are the populations at the highest absolute risk of severe influenza complications — and the groups most likely to respond differently to mRNA-based vaccine platforms. No efficacy or safety data exists for these groups.
4. No co-administration data. MFLUSIVA has not been studied for co-administration with other routinely recommended respiratory vaccines — COVID-19, RSV, and pneumococcal vaccines — which are frequently administered in the same visit, particularly for older adults in fall vaccination programs.
Why This Vote Matters Beyond Moderna
The significance of the MFLUSIVA advisory committee hearing extends beyond a single product and a single company. It is the FDA's first major public evaluation of an mRNA vaccine platform application since the COVID-19 era — and it occurs under a regulatory environment that has, under the current administration, conducted fewer public advisory committee hearings and made more closed-door decisions, as The Briefs noted.
Standard-dose influenza vaccines typically achieve 40–60% efficacy against lab-confirmed influenza in healthy adults — and considerably less in older adults, where immune senescence reduces vaccine response. The case for mRNA influenza vaccines rests on the platform's ability to generate broader and more potent immune responses, particularly relevant for the 65+ population. If MFLUSIVA's immunogenicity superiority over high-dose comparators in the Phase 3 data translates to clinical benefit in the Phase IV confirmatory trial, it would validate mRNA as a superior influenza vaccine platform.
A favorable VRBPAC outcome would also clear a path for Moderna's combination flu/COVID mRNA vaccine, mCombriax (mRNA-1083) — which was withdrawn from FDA review in 2025 after the agency requested more data on its influenza component, the same component being reviewed now. mCombriax has already received European approval.
Frequently Asked Questions
What is MFLUSIVA?
MFLUSIVA (mRNA-1010) is Moderna's investigational mRNA-based seasonal influenza vaccine. It is under FDA review for the prevention of influenza in adults 50 and older. The VRBPAC advisory committee met June 18, 2026, and the FDA's target approval decision date is August 5, 2026. If approved, it would become the first mRNA-based seasonal influenza vaccine in the United States.
How effective is MFLUSIVA?
In Phase 3 Study P304 (40,805 participants), MFLUSIVA showed a relative vaccine efficacy of 26.6% against RT-PCR-confirmed influenza-like illness compared to a standard-dose flu vaccine. When measuring healthcare outcomes (ER visits, hospitalizations, urgent care), efficacy rose to 47.9%. Against Fluzone High-Dose in adults 65+, MFLUSIVA showed superior antibody responses at Day 29 and at six months.
Why does MFLUSIVA need two different approval types for different age groups?
For adults 50–64, Moderna is seeking traditional approval based on clinical efficacy. For adults 65+, the CDC recommends high-dose or adjuvanted vaccines — not standard-dose vaccines — making a head-to-head clinical comparison against standard dose less relevant. Moderna is seeking accelerated approval for this group based on immunogenicity superiority data, with a Phase IV trial required to confirm clinical benefit.
What are the main concerns about MFLUSIVA?
FDA scientists flagged: data from only a single flu season; uncertainty about efficacy against the B/Victoria influenza strain; no data in immunocompromised or very frail elderly individuals; and no co-administration data with other respiratory vaccines. These are all subject to review and post-marketing requirements.
When could MFLUSIVA reach pharmacies?
If the FDA approves MFLUSIVA by the August 5 PDUFA date, it could potentially be available for the 2026–27 influenza season, which typically begins in fall.
