U.S. Health Officials Defend Rejection of Moderna’s Flu Vaccine

The F.D.A.’s refusal to examine the company’s mRNA shot drew widespread criticism from doctors and was divisive within the agency.

The Food and Drug Administration on Wednesday backtracked on its refusal to review Moderna’s mRNA flu vaccine, while making an unusual public defense of its decisions on drug approvals.

Moderna announced on Tuesday that its request to submit an application for approval of the flu mRNA shot had been rejected, despite late-stage trials showing that the product was safe and effective.

The agency’s decision was made by Dr. Vinay Prasad, the top vaccine regulator, who overrode staff recommendations and blocked the process.

But Dr. Marty Makary, the F.D.A. commissioner, suggested during a Fox News interview on Wednesday that the agency might eventually approve the vaccine. He characterized the rejection of Moderna’s application as “part of a conversation that occurs with all drug makers” and said the agency would continue to work with the company.

Federal officials on Wednesday also defended the initial decision.

Andrew Nixon, a spokesman for the Department of Health and Human Services, said the agency had asked Moderna to use a high-dose flu vaccine as a control product in people 65 and older in a large study of the vaccine. The company used a GSK product instead, which Mr. Nixon said had exposed older trial participants “to increased risk of severe illness.”

Moderna disputed that account, outlining a series of meetings with the agency beginning in April 2024 in which officials agreed to a study plan comparing the mRNA vaccine with Fluarix, GSK’s widely used vaccine.

“This was an F.D.A.-approved trial design and the F.D.A.’s communications to Moderna were consistent to us that we could continue through the trial,” said Chris Ridley, a company spokesman.

Within the F.D.A., Dr. Prasad’s decision to reject the application was divisive. He aligned with some junior scientists, but clashed with Dr. David Kaslow, the director of the agency’s Office of Vaccines Research and Review, according to an official familiar with the decision-making.

Earlier on Wednesday on Fox News, Dr. Makary also noted the concern that the company had failed to use the high-dose flu vaccine in some older people. “Some say that the trial that they conducted was unethical” for not offering the best option as a control for seniors, he said.

The F.D.A.’s stance contrasts with statements by Robert F. Kennedy Jr., the nation’s health secretary, who has said that vaccines should be tested against an inert placebo, a position widely rejected by people who study vaccines. Mr. Kennedy long raised concerns as a vaccine activist that the inactive ingredients in vaccines could cause harm and should not be used in human trials.

A senior F.D.A. official said that Mr. Kennedy had not been involved in any aspect of the Moderna flu vaccine review.

Moderna said Blackstone, the private equity company, had invested $750 million for its experimental flu vaccine, including a clinical trial of 41,000 people that concluded that the vaccine was safe and effective for people 50 and older. The mRNA vaccine would enable the company to pivot quickly in the event of a particularly deadly flu strain. It would also allow the company to customize flu vaccines to individual nations more nimbly than the current approach of having one vaccine cover an entire hemisphere.

The rejection by Dr. Prasad is unusual for the agency, which did not often refuse to review a company’s request for approval. Dr. Prasad held a prominent position in academic circles before joining the F.D.A., and was known for his acerbic criticism of what he viewed as overly permissive standards by the agency.

Moderna has encountered a series of setbacks since Mr. Kennedy, a sharp critic of mRNA vaccines, became health secretary. Federal officials canceled a nearly $600 million contract with the company to develop a vaccine for humans against bird flu. Later, the agency cut about $500 million in funds for other mRNA projects, affecting Moderna and other companies. The F.D.A. also tightened the criteria for who should receive the Covid vaccine.

During his career as a vaccine activist, Mr. Kennedy spread misinformation that included testimony to the Louisiana legislature in 2021 claiming that Covid vaccines were the “deadliest vaccine ever made.” He also formally asked the F.D.A. to revoke authorization for the mRNA Covid vaccines about six months into the mass vaccination campaign.

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