FDA approves Moderna's mFlusiva, first mRNA-based flu vaccine in the United States

The FDA has approved Moderna's mFlusiva, the first mRNA-based flu vaccine in the United States, for adults aged 50 and older. In clinical trials of over 40,000 participants, mFlusiva was 27% more effective than standard flu shots. The approval follows a highly unusual dispute in early 2026 where the FDA initially refused to review the application before reversing course. The milestone comes despite ongoing opposition to mRNA technology from HHS Secretary Robert F. Kennedy Jr., who previously canceled $500 million in research funding.

mFlusiva FDA approval

• ▪Moderna expects to make mFlusiva available in the United States for the 2026-2027 fall respiratory virus season
• ▪The Food and Drug Administration granted traditional approval of mFlusiva for adults ages 50 to 64 and accelerated approval for adults ages 65 and older
• ▪The Centers for Disease Control and Prevention's Advisory Committee on Immunization Practices has been blocked from meeting by a federal judge's March 2026 ruling
• ▪Moderna agreed to run a postmarketing clinical trial in adults ages 65 and older to confirm mFlusiva's clinical benefit as a condition of its accelerated approval
• ▪The Food and Drug Administration approved Moderna's mFlusiva on August 5, 2026, making it the first mRNA-based influenza vaccine approved in the United States

mRNA vaccine manufacturing advantages

• ▪Moderna's mRNA-based flu vaccine requires two to three months from strain selection to rollout, compared to approximately six months for traditional egg-based vaccines
• ▪The faster manufacturing timeline of mRNA technology allows scientists to better match circulating influenza strains and update vaccines more efficiently if the virus mutates

Clinical trial efficacy data

• ▪In a smaller study of adults aged 65 and older, mFlusiva generated a strong protective immune response compared to an existing high-dose flu vaccine
• ▪In a late-stage clinical trial of over 40,000 adults, mFlusiva was found to be approximately 27% more effective than a standard-dose flu shot
• ▪Common side effects of mFlusiva observed in clinical trials included injection-site pain, fatigue, headache, muscle or joint pain, and fever

FDA refusal-to-file controversy

• ▪The Food and Drug Administration reversed its refusal and accepted Moderna's amended application approximately one to two weeks after Moderna publicly challenged the decision
• ▪The Food and Drug Administration initially issued a refusal-to-file letter to Moderna in February 2026, declining to review the mFlusiva application
• ▪The Food and Drug Administration's initial refusal stemmed from Moderna comparing mFlusiva to a standard-dose flu shot in adults 65 and older, rather than a high-dose vaccine
• ▪In June 2026, the Food and Drug Administration's independent vaccine advisory committee voted unanimously that the benefits of mFlusiva outweighed its risks

RFK Jr. mRNA criticism

• ▪Health and Human Services Secretary Robert F. Kennedy Jr. has repeatedly criticized mRNA technology, calling COVID-19 vaccines 'the deadliest vaccine ever made.'
• ▪The U.S. Department of Health and Human Services under Robert F. Kennedy Jr. canceled approximately $500 million in funding for 22 mRNA vaccine development projects in August 2025