The Donald Trump administration is casting more doubt on the safety of vaccines, with an internal memo from the Food and Drug Administration linking the deaths of at least 10 children to the COVID vaccine and proposing new regulatory measures as a result.

The memo was obtained by The New York Times and not publicly released. It did not provide details such as the ages of the children, whether they had any health problems or how the agency determined the vaccine-death link. Nor did it disclose the maker of the vaccines involved.

The findings have not been published in a peer-reviewed medical journal, drawing suspicion from some critics of Health Secretary Robert F. Kennedy Jr., who has repeatedly criticized the COVID-19 shots as deadly despite the scientific consensus that they are safe.

The memo was written by Dr. Vinay Prasad, the director of the FDA’s vaccine division. He sent it to agency staff members Friday, outlining findings from a review of reports concerning childhood deaths and attributing them to myocarditis, or inflammation of the heart muscle.

The COVID vaccine, like many other immunizations, carries some health risks in certain cases, and mainstream scientists have been studying the vaccine’s effects on people for years, especially the incidence of myocarditis in teenage boys and young men.

“This is a profound revelation,” Prasad wrote in a memo to staff members. “For the first time, the U.S. FDA will acknowledge that COVID-19 vaccines have killed American children.”

Prasad said he would propose a range of new oversight and review of vaccines, though it was unclear whether the White House had been advised of the memo’s contents. The proposals could be refined by government officials or challenged by lawmakers and drug companies.

A spokesperson for the Department of Health and Human Services, which oversees the FDA, did not respond to a request for comment.

The memo represents another escalation of broadsides on vaccines by federal authorities under Kennedy, who has used his position as secretary to repeatedly raise doubts about inoculations and name other skeptics to positions of authority.

Kennedy’s team has issued new policies that are limiting access to the COVID shots to people 65 and older as well as to younger people with underlying medical conditions. He and FDA officials have also called for more studies of existing vaccines that have been considered safe for decades.

Health officials in the first Trump administration, when the vaccines were developed during the pandemic, and in the Joe Biden years, strongly endorsed the COVID shots as lifesaving measures. Public health experts have pointed to the number of lives saved by the COVID vaccine and to the fact that the virus caused more than 1 million deaths among Americans. About 2,100 children have died of COVID since the pandemic began, according to the American Academy of Pediatrics.