Rare cases of myocarditis (inflammation of the heart muscle) and pericarditis (inflammation of the outer lining of the heart) have been reported after children and teens got a Pfizer-BioNTech COVID-19 vaccine. New studies have shown the rare risk of myocarditis and pericarditis associated with mRNA COVID-19 vaccination—mostly among males between the ages of 12 and 39 years—may be further reduced with a longer time between the first and second dose. Related pages: COVID-19 Vaccine Safety in Children and Teens Myocarditis and Pericarditis After mRNA COVID-19 Vaccination Association Between COVID-19 and Myocarditis Using Hospital-Based Administrative Data — United States, March 2020–January 2021 | MMWR