The FDA sent Moderna a so-called “refusal-to-file” letter, stating that the clinical trials supporting the application did not meet the requirement of being “adequate and well-controlled”. The agency’s concerns focused primarily on how the new vaccine was compared with other influenza vaccines regarded in the United States as the standard of care. The regulator stressed that the decision was not related to the vaccine’s safety or efficacy, but rather to formal issues in the study design.
Moderna said its Phase 3 trials met all primary endpoints and that, in parts of the analysis, its vaccine performed better than the existing standard product. However, the FDA deemed the chosen comparator insufficient. The company has requested a meeting with regulators to determine a possible path forward. Moderna’s flu vaccine is currently under review in the European Union, Canada and Australia, with potential approvals expected in 2026 or early 2027.
The market reaction was immediate. In pre-market trading, Moderna shares fell by more than 10%, reflecting investor concerns about the vaccine’s commercial prospects in the world’s largest pharmaceutical market.
The decision also highlights a broader shift in the U.S. government’s stance on vaccination. In recent months, the FDA — operating under the leadership of Health and Human Services Secretary Robert F. Kennedy Jr., who has repeatedly criticized mRNA vaccines and tightened regulatory standards — has revised recommendations for routine immunizations, including those for influenza. Many medical experts warn that such moves damage public confidence in vaccines and could discourage both manufacturers and the public from investing in and participating in vaccination programs, potentially undermining future efforts to control infectious diseases.
Moderna CEO Stéphane Bancel described the FDA’s refusal to review the mRNA-1010 influenza vaccine as inconsistent with prior discussions. “This decision … does not further our shared goal of enhancing America’s leadership in developing innovative medicines,” he said.
Analysts at Jefferies added that the FDA’s action “raises the risk of a more prolonged regulatory pathway” for both Moderna’s standalone flu vaccine and its combined flu – COVID vaccine. Experts at RBC Capital Markets echoed that view, saying the situation fits a broader pattern in the agency’s current approach. They noted that Moderna’s trial met its primary endpoints in more than 43,000 participants and had been accepted for review in the EU, Canada and Australia — but added that “we struggle to see current FDA leadership reversing course.”