U.S. Federal regulators are reviewing data on the link between Moderna’s coronavirus vaccine and a rare heart problem in adolescents, the company announced Sunday. That side effect — myocarditis, an inflammation of the heart muscle — has also worried advisers to federal agencies in deliberations regarding use of the Pfizer-BioNTech vaccine in younger children and teenagers.

Scientists advising the Centers for Disease Control and Prevention will review the latest data on the condition at a meeting Tuesday before deciding whether to recommend the Pfizer-BioNTech vaccine for younger children.

So how common is myocarditis, really? And should parents be concerned about vaccinating their children?