The approval gives the United States a new tool ahead of the 2026 to 2027 respiratory virus season, after an estimated 45,000 flu-related deaths in the 2024 to 2025 season. The CDC estimates vaccination prevented about 12,000 of those deaths.
Two Approval Pathways For Different Age Groups
The FDA granted traditional full approval for adults ages 50 to 64, based on a phase 3 trial involving more than 40,000 participants across 11 countries. About half received mFLUSIVA, also known as mRNA-1010, and half received a standard-dose licensed flu vaccine. Researchers concluded mFLUSIVA was superior in preventing flu-like illness confirmed by RT-PCR lab tests.
For adults 65 and older, the FDA granted accelerated approval, which requires additional post-approval evidence confirming clinical effectiveness. That decision followed a separate U.S. trial of more than 2,900 adults comparing immune responses to mFLUSIVA against a high-dose inactivated flu shot.
Dr. David Cutler, a board-certified family medicine physician at Providence Saint John’s Health Center in Santa Monica who was not involved in the trials, flagged the distinction. “People ≥65 are the group in which we most want to know whether the vaccine actually prevents hospitalization, pneumonia, and death, rather than simply producing higher antibody levels,” he said.
Why mRNA Production Speed Matters For Flu
Influenza viruses change constantly. Traditional egg-based flu vaccines take at least six months to manufacture, according to the FDA, meaning the virus may have shifted by the time doses reach arms. mRNA vaccines can be produced more quickly, potentially keeping pace with rapidly evolving strains.
Cutler described “a potentially important technological advantage,” noting that mRNA vaccines “can theoretically be redesigned and manufactured more rapidly when influenza strains change. That could become increasingly valuable for influenza, where vaccine-virus mismatch is a perennial problem.”
The mRNA flu vaccine uses similar technology to Moderna’s COVID-19 shot, marking the first time the platform has been cleared for seasonal influenza. Dr. Dung Trinh, an internist at MemorialCare Medical Group and Chief Medical Officer of Healthy Brain Clinic in Irvine, called it “a significant scientific milestone… showing that mRNA technology can be applied beyond COVID-19.”
Safety Profile And Precautions
Moderna reported general side effects in clinical trials including headache, fatigue, joint pain, muscle pain, nausea, vomiting, fever, and chills. Reactions at the injection site also occurred. Rare cases of severe allergic reaction or anaphylaxis are possible.
The company advises patients to tell a healthcare professional before vaccination if they have ever had an allergic reaction to another vaccine, are immunocompromised or taking immune-affecting medication, have had Guillain-Barré syndrome after a flu vaccine, or are pregnant, nursing, or planning pregnancy. People with a history of severe reaction to any ingredient in mFLUSIVA should not receive it.
Not A Replacement For All Flu Shots
Both physicians cautioned against viewing mFLUSIVA as a universal substitute. “This is not as a replacement for every existing flu vaccine, but as another evidence-based option that could ultimately give physicians and patients more choices in protecting people at higher risk from influenza,” Trinh said.
Cutler added that he would want “another season or two of real-world evidence before declaring it superior to the established enhanced vaccines,” given the accelerated approval for those 65 and older.
For the 2026 to 2027 season, Cutler said the most important decision remains getting an appropriate flu vaccine rather than waiting for a “perfect” option.
What Happens Next
Moderna expects mFLUSIVA to be available in the United States for the 2026 to 2027 respiratory virus season. Watch for real-world effectiveness data, particularly for adults 65 and older, who carry the heaviest flu burden and whose approval hinges on confirmatory outcomes evidence. If mRNA flu vaccines hold up in practice, the platform could reshape seasonal influenza response and future pandemic preparedness — a prospect Cutler said may matter “beyond influenza itself.” Patients 50 and older should consult their doctors about which flu vaccine fits their risk profile and timing.
— Aisha Mensah, health desk, AXO News