FDA Refuses Moderna mRNA Flu Vaccine Review; Moderna Fights Back

The FDA issued a rare refusal-to-file letter for Moderna’s mRNA-1010 flu shot over comparator concerns. Moderna calls the move “inconsistent” and politically charged.

The FDA has declined to review Moderna's biologics license application for its seasonal influenza vaccine, mRNA-1010, issuing a rare refusal-to-file (RTF) letter that has ignited a fierce dispute between the company and federal regulators.

The letter, signed by FDA vaccine chief Dr. Vinay Prasad, cites a single technical reason: Moderna's Phase 3 trial used a licensed standard-dose influenza vaccine as its comparator, which the agency now argues "does not reflect the best-available standard of care." The FDA raised no safety or efficacy concerns with the vaccine itself.

Moderna has responded with forceful pushback. CEO Stéphane Bancel stated the decision "is inconsistent with previous written communications" from the FDA, noting that CBER had reviewed and accepted the trial design including the comparator during pre-submission meetings dating back to April 2024. Dr. Stephen Hoge, Moderna's president, called the rejection "a complete stunner."

The decision exposed internal divisions at the FDA. Reports indicate Dr. Prasad overrode agency reviewers who favored proceeding. An HHS spokesman defended the move, claiming Moderna "exposed participants age 65 and over to increased risk" by using a standard-dose comparator instead of a high-dose shot. Moderna disputes this, citing a separate Phase 3 trial in older adults where mRNA-1010 phase -3 clinical trials was compared directly to a high-dose vaccine and met all primary endpoints.

The controversy arrives amid a charged political environment. HHS Secretary Robert F. Kennedy Jr., who appointed Prasad, has long criticized vaccines. Last August, HHS canceled $500 million in mRNA vaccine research funding. Moderna announced in January it would no longer invest in late-stage vaccine trials due to U.S. policy headwinds.

Wall Street reacted swiftly. Moderna shares fell approximately 10% following the announcement. Analysts warn the RTF may also delay the U.S. pathway for mRNA-1083, Moderna's combination COVID-flu vaccine candidate.

The company has requested a Type A meeting with the FDA for reconsideration. Meanwhile, mRNA-1010 remains under active review in the EU, Canada, and Australia, with potential approvals expected in late 2026 or early 2027.