FDA approves Moderna’s mFlu Vaccine

The U.S. Food and Drug Administration (FDA) has approved mFLUSIVA (mRNA-1010), the first messenger RNA (mRNA)-based vaccine for seasonal influenza, marking a significant milestone in respiratory disease prevention . Developed by Moderna, the shot is authorized for adults aged 50 and older and is expected to reach select retailers within weeks, just in time for the 2026-2027 respiratory virus season . The approval arrives amid ongoing public debate over mRNA technology, with Health and Human Services Secretary Robert F. Kennedy Jr., a longtime vaccine critic, having expressed skepticism about the platform .

Clinical Trial Data Demonstrates Superior Efficacy

The approval for adults aged 50 to 64 is based on the Phase 3 FLUENT trial, a randomized, observer-blind, active-controlled study that enrolled 40,805 participants across 301 sites in 11 countries . Participants received either a single dose of the trivalent mRNA-1010 vaccine (37.5 μg) or a licensed standard-dose influenza vaccine comparator, with a median follow-up of 181 days .

The results showed that mRNA-1010 demonstrated a relative vaccine efficacy of 26.6% against RT-PCR-confirmed, protocol-defined influenza-like illness caused by influenza A or B strains, compared with the standard-dose vaccine . Among the 19,260 participants aged 65 and older, the relative vaccine efficacy was 27.4% . The vaccine met prespecified thresholds for noninferiority, superiority, and higher-level superiority .

Two-Tiered Approval Pathway for Older Adults

The FDA granted a bifurcated approval: traditional full approval for adults aged 50 to 64, and accelerated approval for those 65 and older . The accelerated approval for the older cohort is supported by a separate immunogenicity trial involving 2,992 U.S. adults that compared mRNA-1010 against a licensed high-dose quadrivalent influenza vaccine . The mRNA vaccine elicited hemagglutination inhibition antibody titers that were statistically noninferior to, and met prespecified superiority criteria over, the high-dose comparator across all four influenza A and B strains in this age group .

As a condition of accelerated approval, Moderna has committed to conducting a postmarketing confirmatory trial to verify clinical benefit in adults 65 and older . Descriptive relative vaccine efficacy data from the larger FLUENT trial provide additional supporting evidence for this population .

Safety Profile and Side Effects

Moderna reported an acceptable safety profile across the Phase 3 program, with no new safety concerns identified . Solicited adverse events were more common with mRNA-1010 than with standard-dose comparators, including injection-site pain (65.8%), fatigue (45.1%), and headache (37.8%) . However, investigators reported that most adverse events were mild to moderate and transient, typically resolving within one to two days .

Serious adverse event rates were 2.2% in mRNA-1010 recipients versus 1.9% in the standard-dose group . Severe allergic reactions are rare, and mFLUSIVA is contraindicated in individuals with a history of severe allergic reaction to any vaccine component . The vaccine uses the same mRNA platform and lipid nanoparticle delivery system as Moderna's COVID-19 vaccines .

A Contentious Regulatory Journey

The approval caps a review process marked by unusual regulatory friction. In February 2026, the FDA's Center for Biologics Evaluation and Research issued a refusal-to-file letter for Moderna's original application, declining to review it . The agency objected to Moderna's use of a standard-dose influenza vaccine as the comparator in its pivotal trial for participants 65 and older, arguing that this did not represent the "best-available standard of care" for that age group, as the CDC preferentially recommends high-dose or adjuvanted vaccines for seniors . The FDA did not raise concerns about the vaccine's safety or efficacy .

Following public disclosure of the decision and Moderna's objections, the FDA reversed course approximately one week later . Moderna proposed an amended, age-stratified regulatory strategy: full approval for adults 50 to 64 and accelerated approval for those 65 and older, paired with a commitment to conduct postmarketing studies against high-dose comparators . The agency accepted the amended application .

In June 2026, the FDA's Vaccines and Related Biological Products Advisory Committee unanimously voted 9-0 to recommend mRNA-1010 for adults aged 50 and older, concluding that the vaccine's benefits outweighed its risks . This marked the panel's first review of a new vaccine application since May 2023 .

Advantages of mRNA Technology for Influenza

Public health experts have highlighted several advantages of the mRNA platform for influenza vaccination. Unlike traditional flu vaccines, which require approximately six months to manufacture using egg-based or cell-based processes, mRNA vaccines can be produced in two to three months . This faster production timeline could allow for closer matching to circulating strains, particularly if a new influenza strain emerges unexpectedly during the season .

"Flu remains a significant public health challenge, and mFLUSIVA provides an important new option for America's seniors," said Stéphane Bancel, Moderna's chief executive officer . "This approval also reflects the ongoing potential of our mRNA platform to help address important public health challenges through continued scientific innovation" .

Availability and Next Steps

Moderna expects mFLUSIVA supply to be available at select U.S. retailers in the coming weeks, alongside the company's other approved mRNA products: Spikevax (COVID-19 vaccine), mRESVIA (respiratory syncytial virus vaccine), and mNEXSPIKE . The vaccine has also been accepted for regulatory review in the European Union, Canada, and Australia, with additional country submissions planned during 2026 .

For pharmacists and clinicians, the approval introduces a fourth mRNA product to routine immunization discussions. Patients may have questions about side effects, coverage, and availability. Coverage and insurance reimbursement may lag the FDA approval given ongoing disputes over the CDC's Advisory Committee on Immunization Practices, which determines use recommendations . Experts advise against delaying vaccination altogether while waiting for the new option to become more widely available .