The US drug regulator on Friday added a warning to the literature that accompanies Pfizer Inc/BioNTech and Moderna Covid vaccine shots to indicate the rare risk of heart inflammation after its use.

For each vaccine, the fact sheets for healthcare providers have been revised to include a warning that reports of adverse events suggest increased risks of myocarditis and pericarditis, particularly after the second dose and with onset of symptoms within a few days after vaccination, the FDA said.