mRNA Enters the Seasonal Influenza Vaccine Market: FDA Approves Moderna’s mFLUSIVA

mRNA technology has officially joined the seasonal influenza vaccine manufacturing landscape that has remained in place for decades. The U.S. Food and Drug Administration (FDA) approved Moderna’s trivalent influenza vaccine mFLUSIVA for adults aged 50 and older, making it the first mRNA seasonal influenza vaccine licensed in the United States and bringing the platform that gained prominence during the COVID-19 pandemic into routine respiratory disease prevention.

mFLUSIVA uses lipid nanoparticles to encapsulate mRNA, enabling human cells to temporarily produce the influenza virus hemagglutinin antigen. The approved formulation covers influenza A(H1N1), influenza A(H3N2), and B/Victoria lineage strains. Unlike most conventional vaccines grown in chicken eggs, the mRNA manufacturing process does not produce egg-adaptive mutations and could theoretically shorten the time required for strain updates and production. However, whether faster manufacturing can translate into more accurate strain matching each season will still depend on how surveillance, strain selection, and supply systems work together.

The core evidence comes from a Phase 3 study conducted at 301 trial sites across 11 countries, enrolling a total of 40,805 adults aged 50 and older. The study spanned the 2024–2025 Northern Hemisphere influenza season, with participants randomly assigned to receive mFLUSIVA or an approved standard-dose influenza vaccine. Against RT-PCR-confirmed influenza-like illness meeting the trial definition, mFLUSIVA had a relative vaccine efficacy of 26.6%, with a 95% confidence interval of 16.7% to 35.4%. This means the risk of confirmed cases was reduced by approximately another quarter compared with the control vaccine; it does not mean that mFLUSIVA provided an absolute protection rate of 26.6% compared with no vaccination.

The FDA used a split approval pathway: people aged 50 to 64 received traditional approval based on clinical efficacy data, while those aged 65 and older received accelerated approval, based primarily on immune responses induced by mFLUSIVA compared with a high-dose influenza vaccine in another study. Because high-dose, recombinant, or adjuvanted vaccines were already the preferentially recommended options for older adults in the United States, a comparison with a standard-dose vaccine alone is not sufficient to fully answer questions about mFLUSIVA’s relative benefit in real-world care for older adults.

Moderna must therefore conduct a Phase 4 confirmatory study directly comparing mFLUSIVA with the vaccines currently preferentially recommended for older adults over two influenza seasons to verify its clinical benefit. This requirement also highlights the limits of accelerated approval: the current evidence in people aged 65 and older primarily demonstrates that the immune response is comparable or superior, but does not yet establish that mFLUSIVA can reduce more cases of influenza, hospitalizations, or deaths than high-dose or adjuvanted vaccines.

Regarding safety, the FDA review showed that serious adverse events, deaths, and adverse events of special interest were broadly balanced between the two groups, with no safety signal identified that would prevent approval. mFLUSIVA more commonly caused reactions such as injection-site pain, fever, headache, fatigue, and muscle aches. Most were mild to moderate and typically resolved in about two days. The existing data still have clear gaps, including coverage of only one influenza season, insufficient representation of people who are frail or immunocompromised, and a lack of data on coadministration with COVID-19, RSV, or pneumococcal vaccines.

The approval opens the vast seasonal vaccine market to the mRNA platform, but it does not mean the product can immediately secure widespread procurement. U.S. influenza vaccine contracts are generally finalized several months before the vaccination season, and market analysis suggests that Moderna has missed the main 2026 procurement window, with commercial contributions at scale potentially not emerging until the second half of 2027. By then, mFLUSIVA will not only have to compete with established suppliers including Sanofi, GSK, CSL Seqirus, and AstraZeneca, but will also need to use data across multiple seasons and from the real world to demonstrate that the speed advantage of mRNA manufacturing delivers measurable public health benefits.