The FDA issued a refuse-to-file letter for the product, known as mRNA-1010, even though the company had used a priority review voucher to speed up the application's review.

The only reason cited for the refusal is the choice of a licensed standard-dose seasonal flu vaccine as the comparator. The CBER letter points to the absence of an "adequate and well-controlled” study with a comparator arm that "does not reflect the best available standard of care.”

Meanwhile, Moderna pushed back, arguing that neither current regulations nor the FDA's industry guidance refers to using a comparator that reflects "the best available standard of care.” The company also said the letter does not identify any specific safety or efficacy issues related to mRNA-1010.

Moderna decries regulatory inconsistency

The company also cites regulatory inconsistency, noting that in April 2024, during a pre-Phase 3 consultation, the CBER stated in writing that it would be "acceptable to use a licensed standard-dose influenza vaccine as a comparator,” while recommending (without requiring) the use of preferred vaccines for those over 65 (such as Fluozone HD or Fluad).

Moderna added that in August 2025, after its Phase 3 trial succeeded (primary endpoints met), it held a pre-submission meeting. At that time, the CBER requested additional supportive analyses, but never indicated it would refuse to review the filing.

Moderna Chief Executive Officer Stéphane Bancel said: "This CBER decision, which raises no concerns about the safety or efficacy of our product, does not serve our shared goal of strengthening America's leadership in innovative drug development.” He added: "It should not be controversial to conduct a full review of an influenza vaccine submission using an FDA-approved vaccine as a comparator in a study discussed and agreed with the CBER before it began.”

The company said next steps include an emergency meeting with the CBER to understand the basis for the refusal, while internationally the product has been accepted for review in the European Union, Canada and Australia.

Finally, Moderna said the refusal should not affect its financial guidance.

Analysts react

Jefferies said the delay to mRNA-1010 could affect the US submission timeline for the combination vaccine (mRNA-1083). The US investment bank's analysts added that the decision could complicate the company's goal of reaching breakeven in 2028, as the vaccine was a key growth driver. Jefferies' main question is whether Moderna will choose to continue the program if the FDA asks for a new Phase 3 study, given that the group's CEO recently said he does not plan new investments in Phase 3 vaccine studies. Jefferies maintains its Hold rating on Moderna shares, with a $42 target price.

At UBS, the CBER decision came as little surprise. Analysts have already warned that flu vaccines will continue to face high-risk regulatory visibility, as the FDA remains clearly very demanding on approval standards for these programs (respiratory vaccines). As a result, UBS had low expectations for this vaccine, meaning it is not really built into future growth models or the consensus.

For the Swiss bank's analysts, the FDA is likely to require a new Phase 3 study against a high-dose vaccine, which Moderna probably will not fund and will not seek to launch in the short term. UBS maintains its Neutral rating on Moderna shares, with a $34 target price.