(Published Aug. 25, 2021 Updated Sept. 1, 2021)

Although the study did not break down the myocarditis risks by age or by sex, the median age of people who developed the condition after vaccination was 25, and 19 of the 21 cases were in males, the researchers reported.

In addition to myocarditis, the Pfizer vaccine was also associated with an increased risk of swollen lymph nodes, appendicitis and shingles, although all three side effects remained uncommon in the study.