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.
As VAERS reporting normalizes following the COVID-19 pandemic surge, the data landscape for myocarditis safety signal analysis is shifting. Annual VAERS reports in 2025-2026 have returned to the 35,000-45,000 range typical of the pre-pandemic era (2015-2019), making year-over-year comparisons more meaningful again.
The HHS administration has signaled increased focus on vaccine safety data analysis, including the development of AI-powered tools for pattern detection in VAERS reports. While these tools are still under development, they represent a potential evolution in how adverse event data is analyzed and interpreted.
New vaccines entering the market — including RSV vaccines for older adults and pregnant women, updated COVID-19 formulations, and potential H5N1 avian flu vaccines — continue to add new data streams to VAERS. Each new vaccine type provides additional context for understanding myocarditis safety signal analysis across the full spectrum of vaccine safety surveillance.
This analysis is based entirely on VAERS passive surveillance data, which carries important limitations that must be understood:
For these reasons, VAERS data is best used for signal detection — identifying potential safety concerns that warrant further investigation — rather than for definitive risk assessment. When VAERS surfaces a potential signal, it is investigated using more rigorous systems like the Vaccine Safety Datalink (VSD) and controlled epidemiological studies.
All data on VaccineWatch comes from the official VAERS public-use datasets published by the CDC and FDA. Our current dataset covers reports from 1990 through early 2026. We process the raw data without filtering or editorializing — every metric is a transparent aggregation of official government data.
As VAERS reporting normalizes following the COVID-19 pandemic surge, the data landscape for myocarditis safety signal analysis is shifting. Annual VAERS reports in 2025-2026 have returned to the 35,000-45,000 range typical of the pre-pandemic era (2015-2019), making year-over-year comparisons more meaningful again.
The HHS administration has signaled increased focus on vaccine safety data analysis, including the development of AI-powered tools for pattern detection in VAERS reports. While these tools are still under development, they represent a potential evolution in how adverse event data is analyzed and interpreted.
New vaccines entering the market — including RSV vaccines for older adults and pregnant women, updated COVID-19 formulations, and potential H5N1 avian flu vaccines — continue to add new data streams to VAERS. Each new vaccine type provides additional context for understanding myocarditis safety signal analysis across the full spectrum of vaccine safety surveillance.
This analysis is based entirely on VAERS passive surveillance data, which carries important limitations that must be understood:
For these reasons, VAERS data is best used for signal detection — identifying potential safety concerns that warrant further investigation — rather than for definitive risk assessment. When VAERS surfaces a potential signal, it is investigated using more rigorous systems like the Vaccine Safety Datalink (VSD) and controlled epidemiological studies.
All data on VaccineWatch comes from the official VAERS public-use datasets published by the CDC and FDA. Our current dataset covers reports from 1990 through early 2026. We process the raw data without filtering or editorializing — every metric is a transparent aggregation of official government data.
As VAERS reporting normalizes following the COVID-19 pandemic surge, the data landscape for myocarditis safety signal analysis is shifting. Annual VAERS reports in 2025-2026 have returned to the 35,000-45,000 range typical of the pre-pandemic era (2015-2019), making year-over-year comparisons more meaningful again.
The HHS administration has signaled increased focus on vaccine safety data analysis, including the development of AI-powered tools for pattern detection in VAERS reports. While these tools are still under development, they represent a potential evolution in how adverse event data is analyzed and interpreted.
New vaccines entering the market — including RSV vaccines for older adults and pregnant women, updated COVID-19 formulations, and potential H5N1 avian flu vaccines — continue to add new data streams to VAERS. Each new vaccine type provides additional context for understanding myocarditis safety signal analysis across the full spectrum of vaccine safety surveillance.
This analysis is based entirely on VAERS passive surveillance data, which carries important limitations that must be understood:
For these reasons, VAERS data is best used for signal detection — identifying potential safety concerns that warrant further investigation — rather than for definitive risk assessment. When VAERS surfaces a potential signal, it is investigated using more rigorous systems like the Vaccine Safety Datalink (VSD) and controlled epidemiological studies.
All data on VaccineWatch comes from the official VAERS public-use datasets published by the CDC and FDA. Our current dataset covers reports from 1990 through early 2026. We process the raw data without filtering or editorializing — every metric is a transparent aggregation of official government data.