Dr. Vinay Prasad, the director of the Food and Drug Administration’s vaccine division, sent a memo to staff that linked children’s deaths to the COVID-19 vaccine, but did not provide data to back the claim.

The memo said that a review “found that at least 10 children have died after and because of receiving COVID-19 vaccination,” according to multiple sources familiar with the email. The memo was first reported by the New York Times.

Prasad suggested that the deaths were related to myocarditis, or the inflammation of the heart muscle. Prasad did not share any data used in the review, including the children’s ages, whether they had existing health conditions, or how the FDA determined there was a link between their death and the vaccine. The findings were not published in a peer-reviewed medical journal.

Myocarditis has been linked to the COVID-19 vaccine, but studies have largely confirmed that the risk of the condition is significantly higher after a coronavirus infection, pediatric cardiologists told CBS News in 2023. The prognosis following myocarditis due to the vaccine is also better than from infection, studies show. COVID-19 infection is also linked to other long-term complications.

The risk of myocarditis appears to be higher when vaccine doses are given closer together, as was the case when the vaccines first hit the market. Now, most people receive each dose of the vaccine about a year apart. If someone receives the primary series before age 5, the risk virtually disappears.