Moderna says Covid vaccine has fewer breakthrough cases than Pfizer’s, but higher myocarditis rates in young men

Moderna defended the use of its Covid-19 vaccine Thursday, saying the protection it offers against severe disease, hospitalization and death outweighs the risk of myocarditis, a rare heart condition seen in a small number of young men who received the shot.

The company announced last week that the Food and Drug Administration needed more time to decide whether to authorize its two-dose vaccine for use in children ages 12 to 17 as the agency looks into reports of myocarditis, or the inflammation of the heart muscle.

Reported cases of the rare heart inflammation...