The US Food and Drug Administration will now require Covid-19 vaccines from Pfizer/BioNTech and Moderna to use expanded warning labels with more information about the risk of a rare heart condition after vaccination.

The Food and Drug Administration says it has decided to continue approving COVID-19 vaccine updates for seniors and others at higher risk of severe disease, but will require vaccine makers to conduct major new clinical trials before approving them for wider use.

According to the CDC, cases of myocarditis and pericarditis are rare with the vaccines and in most cases resolve within a few days of dosing. None of the companies involved have commented on the change in the warning text.