Moderna Inc. (MRNA) had a rough Wednesday after receiving a refusal-to-file letter from the U.S. Food and Drug Administration regarding its investigational influenza vaccine, mRNA-1010. The FDA's decision sent shares tumbling, though the setback appears to be more about regulatory bureaucracy than actual concerns about the vaccine itself.

"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.

The Comparator Controversy

The FDA's Center for Biologics Evaluation and Research (CBER) informed Moderna that it wouldn't even begin reviewing the biologics license application for mRNA-1010. The sole reason? The company's choice to use a standard-dose seasonal influenza vaccine as a comparator in its clinical trials.

The refusal letter specifically cited the lack of an "adequate and well-controlled" study with a comparator arm that "does not reflect the best-available standard of care." Here's where things get interesting: neither the relevant regulation governing adequate and well-controlled studies nor the FDA's own guidance for seasonal influenza vaccines mentions anything about using a comparator that reflects the "best-available standard of care." And notably, the letter didn't identify any specific safety or efficacy concerns regarding mRNA-1010.

Moderna has requested a Type A meeting with CBER to understand what's going on and doesn't expect any impact on its 2026 financial guidance.

A Regulatory About-Face

What makes this particularly frustrating for Moderna is that the refusal seems to contradict previous communications from the FDA. In April 2024, when Moderna submitted its Phase 3 study protocol during a pre-Phase 3 consultation, CBER provided written guidance stating that "while we agree it would be acceptable to use a licensed standard dose influenza vaccine as the comparator in your Phase 3 study, we recommend you use a vaccine preferentially recommended for use in older adults by the ACIP for participants >65 years of age in the study."

ACIP-recommended vaccines include Sanofi SA's (SNY) Fluzone HD and Flublok, along with Seqirus Inc.'s Fluad.

After Moderna submitted the protocol in April 2024, CBER didn't raise any objections or clinical hold comments about the adequacy of the Phase 3 trial. The study launched in September 2024 without any red flags from regulators.

Fast forward to August 2025: after completing the Phase 3 efficacy trial—in which mRNA-1010 met all agreed-upon pre-specified primary endpoints—Moderna held a pre-submission meeting with CBER. In written feedback from that meeting, CBER requested additional supportive analyses on the comparator and indicated the data would be a "significant issue during review of your BLA." Moderna provided those additional analyses in its submission, including data from a separate Phase 3 trial comparing mRNA-1010 against a licensed high-dose influenza vaccine. At no point in the pre-submission feedback or meeting did CBER suggest it would refuse to review the file entirely.

International Reception Looks Better

While the FDA balks, other regulatory bodies seem more accommodating. The vaccine has been accepted for review in the European Union, Canada, and Australia, with potential approvals expected to begin in late 2026 or early 2027. Moderna plans to submit applications in additional countries throughout 2026.

The Stock Takes a Hit

Currently, Moderna is trading 12.8% below its 20-day simple moving average and 7% above its 50-day simple moving average, indicating some short-term weakness alongside longer-term strength. Over the past 12 months, shares have increased by 35.77%, and the stock remains positioned closer to its 52-week highs than lows—suggesting relatively strong performance despite recent volatility.

From a momentum perspective, the stock has been outperforming the broader market with a strong score of 89.26. The setup reveals what traders call a "high-flyer" pattern, though the recent regulatory challenges highlight the need for careful monitoring going forward.

Moderna shares were down 8.44% at $38.45 during premarket trading on Wednesday.