Moderna Inc. (NASDAQ:MRNA) stock fell Wednesday as the company faced a setback following a refusal-to-file letter from the U.S. Food and Drug Administration (FDA) regarding its investigational influenza vaccine, mRNA-1010.

“This decision by CBER, which did not identify any safety or efficacy concerns with our product, does not further our shared goal of enhancing America’s leadership in developing innovative medicines,” said Stéphane Bancel, CEO of Moderna.

Regulatory Setback

The FDA’s Center for Biologics Evaluation and Research (CBER) notified Moderna that it would not initiate a review of the biologics license application for mRNA-1010, citing the choice of a standard-dose seasonal influenza vaccine as a comparator as the sole reason for the refusal.

Moderna has requested a Type A meeting with CBER to understand the basis for the refusal and does not expect any impact on its 2026 financial guidance.

Specifically, the letter cited the lack of an “adequate and well-controlled” study with a comparator arm that “does not reflect the best-available standard of care.”

Neither the relevant regulation (Adequate and well-controlled studies) nor the FDA’s guidance for industry on seasonal influenza vaccines contains any reference to the use of a comparator reflecting the “best-available standard of care.” The letter did not identify any specific safety ...