Silver Spring, Maryland - A dozen former officials from the US Food and Drug Administration on Wednesday said they were "deeply concerned" about possible vaccine policy changes after the leaking of a document linking Covid-19 vaccines to children's deaths.

The warning, published in the respected New England Journal of Medicine, follows the leak days earlier of an internal FDA memo casting doubt on the safety of Covid-19 vaccines and calling for a change to existing procedures.

"We are deeply concerned by sweeping new FDA assertions about vaccine safety and proposals that would undermine a regulatory model designed to ensure that vaccines are safe, effective, and available when the public needs them most," wrote the 12 doctors, all of whom have previously held senior FDA positions under both Democratic and Republican administrations.

The controversy comes as President Donald Trump has placed the country's health policy under Health Secretary Robert F. Kennedy Jr., a vocal vaccine skeptic who has frequently spread unfounded conspiracy theories about such medication.

The leaked document, signed by current senior FDA official Vinay Prasad, said that Covid-19 vaccines were linked to the deaths of at least 10 children, according to an unpublished internal analysis.

It calls for a review of the approval procedures for certain vaccines, including those against influenza.

Vaccines against Covid-19 are considered safe and effective by global health authorities, and protect against the most severe forms of the infection.

According to the former FDA officials, "the memo 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."

Kennedy has reshaped federal health agencies since taking office, carrying out mass layoffs and appointing polarizing figures to senior roles.

Kennedy has a long history of promoting dubious claims, many of which have become articles of faith among adherents to his "Make America Healthy Again" movement, a vital part of President Donald Trump's fractious Make America Great Again coalition.

The Department of Health and Human Services and the FDA did not respond to AFP requests for comment on the leaked memo.