FDA Approves Moderna's mFLUSIVA, First mRNA-Based Seasonal Flu Vaccine, for Adults 50 and Older
Key Insights
The FDA approved Moderna's mFLUSIVA (search) in August 2026, making it the first seasonal influenza (search) vaccine in the US to use mRNA-based production.
In a phase 3 trial of more than 40,000 adults aged 50 and older, 2% of mFLUSIVA (search) recipients developed flu illness versus 2.8% on a standard-dose vaccine.
mFLUSIVA (search) encodes full-length hemagglutinin (search) from three WHO-recommended influenza (search) strains delivered by lipid nanoparticles, and the 2026-27 formula contains no egg protein.
The US Food and Drug Administration (search) approved Moderna's mRNA-based seasonal influenza (search) vaccine in August 2026 for adults aged 50 to 64, with the approval also covering people in the 65-and-older age group. Named mFLUSIVA (search), the product is the first seasonal flu vaccine to use mRNA-based production, a manufacturing approach that allows vaccines to be updated quickly to match circulating influenza strains.
How the vaccine is designed
mFLUSIVA (search) carries mRNA encoding full-length viral hemagglutinin (search) surface glycoproteins from three influenza (search) strains recommended by the World Health Organization. The sequences are packaged in lipid nanoparticles that deliver the payload into cells, where the mRNA is translated into hemagglutinin proteins. The immune system recognizes these proteins as foreign and mounts responses that protect against influenza.
The mRNA breaks down naturally after delivering its instructions and does not enter the cell nucleus or alter DNA. The vaccine contains no whole flu virus and cannot cause influenza (search). The 2026-27 formula contains no egg protein, antibiotics or preservatives.
The approach differs from traditional flu shots, which may contain inactivated virus or purified viral proteins and are made using egg-based, cell-based or recombinant manufacturing. Because viral mRNA sequences are easier to copy than growing large amounts of influenza (search) virus in a lab, manufacturers may be able to update seasonal vaccines more quickly and respond faster when new strains emerge.
Phase 3 efficacy data
In a phase 3 trial, more than 40,000 adults aged 50 and older received either mFLUSIVA (search) or a licensed, standard-dose, inactivated flu vaccine. Influenza (search) illness developed in 2% of mFLUSIVA recipients compared with 2.8% of those who received the standard-dose vaccine, a relative risk reduction of about 27%.
In two clinical trials, mFLUSIVA (search) outperformed GlaxoSmithKline's four-strain influenza (search) vaccine Fluarix in preventing influenza infection or eliciting antibody responses.
Trial participants included adults more likely to develop serious complications from flu, which is why the vaccine is currently approved only for people aged 50 and older.
Reactogenicity profile
About 75% of mFLUSIVA (search) recipients reported at least one expected short-term reaction, compared with 47% of those who received the standard-dose vaccine. The most common reactions were tenderness at the injection site, mild fatigue, headache, muscle or joint aches, chills, and underarm tenderness or swelling. Most side effects were mild or moderate and lasted around two days.
Position in the adult vaccination schedule
For adults aged 50 to 64, the CDC does not prefer one licensed, age-appropriate flu vaccine over another. mFLUSIVA (search) is one option alongside inactivated and recombinant vaccines, with medical history, availability, prior reactions and personal preference guiding the choice.
Recommendations become more specific at age 65. The CDC has historically recommended one of three enhanced vaccines for this group: Fluzone High-Dose inactivated vaccine, Flublok recombinant vaccine, or Fluad adjuvanted vaccine. mFLUSIVA (search) is now approved for this age group as well.
The CDC estimates that flu infections in the US cause 120,000 to 710,000 hospitalizations and 6,300 to 52,000 deaths each year. Older adults, people with compromised immune systems and children are most at risk. The CDC recommends that most eligible people be vaccinated in September or October, since the immune system needs about two weeks to build protection and vaccinating too early can allow protection to wane before the season ends.
Adults at higher risk of serious flu complications include those aged 50 or older, particularly 65 and older; children under 5; people who are pregnant or gave birth within the past two weeks; those with chronic conditions such as asthma, chronic obstructive pulmonary disease, heart disease, diabetes, kidney or liver disease, a blood disorder or a neurologic condition; people with weakened immune systems; residents of nursing homes or long-term care facilities; and those with a body mass index of 40 or higher.
mRNA technology has been studied since the 1960s and has been proven safe and effective in human medicine since the early 2000s. Vaccines using the platform helped save hundreds of thousands of lives during the COVID-19 pandemic, and the technology is currently being tested in a new treatment for melanoma (search).