A U.S. Food and Drug Administration (FDA) logo, a syringe and a vial are seen in this illustration taken May 13, 2025. REUTERS/Dado Ruvic/Illustration

NEW YORK, Dec 3 (Reuters) - Twelve former U.S. FDA commissioners said on Wednesday they were deeply concerned about proposed changes to U.S. vaccine regulation by the agency's chief scientific officer and the details of his assertion that the COVID-19 vaccine killed 10 children.

The commissioners were responding to an email sent last week by Vinay Prasad, U.S. Food and Drug Administration chief medical and scientific officer, in which he told agency staffers that COVID-19 vaccinations probably contributed to the deaths of at least 10 children who died of heart inflammation but provided few details on how the analysis of those cases was performed.

Prasad also outlined planned changes to regulation of vaccines, including annual flu shots, saying that companies must prove that vaccines work through randomized trials rather than ones that demonstrate the shots elicit an immune response.

"The proposed guidelines would dramatically change vaccine regulation on the basis of a reinterpretation of selective evidence and by a process that breaks sharply with the norms that have anchored the FDA’s globally respected scientific integrity," the former FDA commissioners, who served under both Republican and Democratic presidents, wrote in a piece published in the New England Journal of Medicine.

The authors include Scott Gottlieb and Brett Giroir, who served as commissioners during President Donald Trump's last term.

Prasad did not immediately respond to a request for comment.

Prasad's memo, the commissioners wrote, "offered no explanation of the process and analyses that were used to reach the new retrospective judgment, nor did it indicate why that assessment should justify wholesale rewriting of vaccine regulation."

Prasad was hired by Health Secretary Robert F. Kennedy Jr., a long-time anti-vaccine activist, who has been working to remake U.S. vaccine policy and has called for placebo-based trials of vaccines in the past. Many scientists say it is not typically possible to run such trials for ethical reasons.

(Reporting by Michael Erman; editing by Diane Craft)