evidence: Previous research from around the world, including reports from the Centers for Disease Control and Prevention, has shown a potential increased risk of myocarditis after receiving an mRNA COVID-19 vaccine. [...] The analysis showed people infected with COVID-19 before receiving a vaccine were 11 times more at risk for developing myocarditis within 28 days of testing positive for the virus. But that risk was cut in half if a person was infected after receiving at least one dose of a COVID-19 vaccine. The risk for myocarditis increased after receiving the first dose of the AstraZeneca vaccine, and after a first, second and booster dose of the Pfizer or Moderna vaccine. But the risk of myocarditis associated with the vaccine was lower than the risk associated with COVID-19 infection before or after vaccination – with one exception. Men under 40 who received a second dose of the Moderna vaccine had a higher risk of myocarditis following vaccination. The Pfizer and Moderna mRNA vaccines are available in the U.S.