Important: VAERS reports alone cannot determine if a vaccine caused an adverse event. Reports may contain incomplete, inaccurate, or unverified information. Correlation does not equal causation.
Understanding the most closely-watched vaccine safety signal of the COVID-19 era. Myocarditis (inflammation of the heart muscle) became a major focus of vaccine safety surveillance.
Myocarditis is inflammation of the heart muscle (myocardium). It can be caused by viral infections, autoimmune diseases, drugs, and other factors. Symptoms range from mild chest pain to heart failure. Most cases resolve on their own, though some can be serious.
After the rollout of COVID-19 mRNA vaccines, myocarditis emerged as a recognized rare side effect, particularly in young males after the second dose. The FDA and CDC added a warning label to the Pfizer and Moderna vaccines in June 2021 after reviewing VAERS data and clinical evidence.
COVID-19 vaccines account for 7,695 of the vaccine-myocarditis associations in VAERS — the overwhelming majority. This is not surprising given:
The myocarditis safety signal is actually a success story for vaccine safety surveillance. Here's how it played out:
While COVID-19 dominates the data, myocarditis has been reported with other vaccines as well. Smallpox vaccine (1,053 associations) has a well-documented association with myocarditis. This was known before COVID-19 and is one reason smallpox vaccination is limited to specific populations.
Among myocarditis VAERS reports, 66.7% involved hospitalization and 4.4% reported death. The high hospitalization rate reflects that myocarditis is inherently a condition requiring medical attention. However, it's important to note that most vaccine-associated myocarditis cases in clinical studies were mild and resolved within days to weeks.