FDA rejects Moderna's mRNA flu vaccine application - for reasons with no basis in the law

The Food and Drug Administration (FDA) has refused to review a request from the biotech company Moderna to approve its new flu vaccine. This vaccine utilizes messenger RNA (mRNA), a modern technology. The agency made this decision public on February 10, 2026, via a statement from Moderna. This action is part of a broader effort by federal health leaders to change how vaccines are approved and how the public perceives them.

Under the leadership of Health and Human Services Secretary Robert F. Kennedy Jr., health officials are taking steps to disrupt long-standing public health practices and reshape public perception of vaccine safety. mRNA technology gained prominence at the start of the COVID-19 pandemic. Researchers are now using this same technology to create vaccines for other diseases, including treatments for serious conditions like cancer and autoimmune disorders. This Nobel Prize-winning technology is particularly useful for flu shots, as scientists can create these vaccines quickly each year to match changing influenza virus strains.

However, Secretary Kennedy and other officials, including those at the FDA, have expressed strong doubt regarding mRNA vaccines. They have raised safety concerns without providing solid data to support these risks and have cut funding for research on developing these vaccines.

To explain the importance of the FDA's recent decision, The Conversation spoke with Ana Santos Rutschman, a law professor at Villanova University and an expert on vaccine policy. She explained how this decision fits into the rapidly changing landscape of public health regulations.

In December 2025, Moderna submitted a formal request to the FDA for approval of an mRNA flu vaccine for adults aged 50 and older. The vaccine had been tested in clinical trials involving more than 40,000 people. In response, the agency sent Moderna a letter dated February 3, 2026. This letter was a "refusal-to-file" notice, a type of communication sent when a regulator believes a new drug or vaccine application is incomplete.

It is very rare for the FDA to take this action. Companies that develop new products usually meet with the FDA early on to agree on the requirements for approval. Furthermore, the FDA rarely differs significantly from other major drug regulators worldwide. In this specific case, drug regulators in Canada, Europe, and Australia all accepted Moderna's application for review.

What is especially concerning is that several FDA scientists confirmed they expected to review the Moderna application. David Kaslow, the director of the FDA's Office of Vaccines Research and Review, wrote a memo recommending the review. However, Vinay Prasad, who leads the center overseeing vaccine research, overruled this decision. Directors rarely overrule agency scientists, especially when it involves vaccines. Yet, this is at least the fourth time Prasad has done so since his appointment to the FDA in 2025.

Moderna took an unusual step by announcing the FDA's refusal and releasing the official letter. The letter states that Moderna did not conduct an "adequate and well-controlled" study. The agency claimed this was because Moderna did not compare patients who received the vaccine to patients receiving what the agency called "the best-available standard of care."

In the United States, standard-dose flu vaccines are approved for everyone over 6 months old. However, health authorities recommend that adults over 65 receive a stronger, more potent dose. Moderna's announcement quoted the language the FDA used when it approved the company's clinical trial plan in 2024. Originally, the agency suggested that for people aged 65 and older, the company should compare the effectiveness of its vaccine to the stronger dose. After reviewing Moderna's plan, the FDA had deemed the standard vaccine "acceptable."

The FDA agreed to the trials Moderna conducted. Therefore, the agency's claim that the company did not use the best standard of care is problematic. This claim does not reflect the actual legal requirements for vaccine approval. Although this phrase sounds official, it does not appear anywhere in FDA law or guidance for companies developing vaccines.

Instead, FDA law requires a company to provide data from "adequate and well-controlled studies." Using standard-dose flu vaccines aligns with this requirement because they are widely used across all age groups.

Shortly after Moderna announced the refusal, the news outlet STAT quoted an unnamed FDA official. This official stated that if Moderna showed "some humility," the agency might review the application. However, this review would only be for people under 65. Imposing this restriction after refusing to review the application has no basis in the law. The FDA approves clinical trial parameters early on in consultation with companies.

From a legal perspective, the FDA's decision could be considered "arbitrary and capricious." This means the agency changed its position without a valid reason. If a court makes this determination, it could invalidate the FDA's decision. However, that legal process would take a significant amount of time.

This is the first time the FDA has attempted to prevent the review of a vaccine for reasons not related to safety or effectiveness. This move fits into a broader strategy by federal health officials under Kennedy. It signals an escalation in the agency's efforts to intervene in established procedures for testing vaccines.

In April 2025, Kennedy announced that new vaccines would require additional clinical trials. In November 2025, Prasad released an internal FDA memo claiming that mRNA-based COVID-19 vaccines had killed children. He provided no evidence for this claim. He stated that, in response to these alleged deaths, large-scale changes to vaccine approval requirements were coming.

The FDA's refusal of Moderna's application appears to be Prasad's policy in action.

On a practical level, the FDA is now stating requirements that do not exist in the law. This creates major uncertainty for companies with pending or upcoming vaccine applications. Manufacturers now worry that they might invest resources in the long and difficult process of developing a vaccine, only to receive similarly unpredictable refusals.

More broadly, with so much turmoil in vaccine law and policy, incentives for manufacturers to bring vaccines to market are shrinking. In January 2026, even before the flu vaccine refusal, Moderna's chief executive officer stated the company was scaling back on vaccine development.

Finally, the FDA's move risks fueling further mistrust in vaccines. This aligns with a wider push from federal health officials to question long-settled science.

The situation highlights a significant shift in how the government approaches public health. The decision to reject a widely supported application without clear legal grounds suggests that future vaccine development may face unexpected hurdles. Companies must now navigate a landscape where rules can change based on internal memos rather than established statutes. This uncertainty could slow the pace of medical innovation and limit access to new treatments for serious diseases. The public also faces the challenge of understanding these complex changes when trust in health institutions is at stake. As the legal and political debates continue, the impact on the future of vaccine approval will remain a critical issue for families and policymakers alike.