Moderna says the FDA has declined to review its application for an experimental flu vaccine, a decision the company disclosed on Tuesday that sent ripples through both the biotech industry and financial markets. The move marks another moment in what many see as a broader tightening of vaccine regulations in the United States.
The U.S. Food and Drug Administration declined to begin reviewing Moderna’s application for its experimental flu vaccine, prompting the drugmaker’s shares to drop by about 7% in after-hours trading.
According to Moderna, the FDA’s refusal came as a surprise and conflicted with feedback the company had received earlier—before formally submitting the application and launching Phase 3 clinical trials for the shot, known as mRNA-1010. Moderna said it has since asked for a meeting with the agency to better understand what steps are required to move forward.
Dispute Over Trial Design, Not Safety
Moderna emphasized that the FDA did not raise any safety or effectiveness concerns about the vaccine itself. Instead, the agency objected to the clinical trial’s design, even though that design had previously been discussed and accepted. The company also noted that the setback will not affect its financial outlook for 2026.
Last year, Moderna reported positive Phase 3 results for mRNA-1010, stating that the vaccine met all primary trial objectives. At the time, the company highlighted the standalone flu shot as a crucial building block toward developing a combined influenza and Covid-19 vaccine.
Policy Shifts and Regulatory Scrutiny
The decision comes amid sweeping changes in U.S. immunization policy over the past year under Health and Human Services Secretary Robert F. Kennedy Jr., who has long been known for his skepticism toward vaccines.
Moderna also pointed to Vinay Prasad, the FDA’s top vaccine regulator and head of the Center for Biologics Evaluation and Research (CBER). Prasad, who returned to the agency in August after previously being removed, has publicly advocated for stricter vaccine regulations and has made controversial statements linking child deaths to Covid-19 vaccines.
In a letter dated February 3 and signed by Prasad, the FDA stated that the sole reason for declining to review Moderna’s application was the way its clinical trial was structured.
FDA and Moderna at Odds
The agency specifically criticized Moderna’s choice to compare its vaccine to a standard, already approved flu shot. According to the FDA, this comparator “does not reflect the best-available standard of care,” meaning the trial failed to meet the definition of an “adequate and well-controlled” study.
Moderna strongly disagreed, arguing that FDA rules do not require companies to use the most advanced or highest-dose vaccine as a comparator. The company maintained that its approach complied with existing regulatory guidance.
“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,” Moderna CEO Stéphane Bancel said in a statement. He added that using an FDA-approved flu vaccine as a comparator should not be controversial, especially when the study design had been discussed and agreed upon before trials began.
What Comes Next
Moderna now expects that the earliest possible approval for its flu vaccine would come in late 2026 or potentially 2027, depending on regulatory reviews not only in the U.S. but also in Europe, Canada, and Australia.
For its part, the FDA said it does not comment on regulatory communications involving individual companies, leaving the dispute unresolved for now.
