The FDA will add a warning about rare cases of heart inflammation in adolescents and young adults to fact sheets for the Pfizer/BioNTech and Moderna COVID-19 vaccines, as reported by the National Post.

US Centers for Disease Control and Prevention (CDC) advisory groups found the risk of the heart condition in adolescents and young adults to be likely linked to the vaccines, however the benefits of the shots appeared to clearly outweigh the risk.

"Based on the available data, a warning statement in the factsheets for both medical supplies suppliers and vaccine recipients and caregivers would be warranted," said FDA official Doran Fink at the advisory committee meeting, adding that the regulator expects to move quickly to add the warning after the meeting concludes.

Heart inflammation cases appear to be higher in the week after the second vaccine dose and in males. The CDC identified 309 hospitalizations from heart inflammation in people under 30 years old. Tom Shimabukuro, deputy director of the CDC’s Immunization Safety Office, said that data from one of the agency’s safety monitoring systems suggests a rate of 12.6 cases per million in the three weeks after the second dose in 12- to 39-year-olds.

The CDC said it was still assessing the risk and did not specifically confirm a causal relationship between the vaccines and the heart condition. However, it said that a much-higher-than expected number of young men between the ages of 12 and 24 have experienced heart inflammation after their second dose.

According to data from the US Vaccine Adverse Event Reporting System, there were 347 observed cases of heart inflammation in the week after the second vaccine dose in males aged 12 to 24. According to the CDC, that compares with expectations of 12 or fewer cases for males in that age range based on US population background incidence rates.