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.

In another sign of growing scrutiny over Covid-19 vaccines, the Food and Drug Administration has asked the two makers of mRNA vaccines to widen the age range of boys and young men that their labels say are at risk for a rare side effect causing heart inflammation.