Fact check: How does myocarditis risk after Pfizer vaccination compare to myocarditis risk after SARS-CoV-2 infection across age groups in 2021-2023?

Executive Summary — direct answer up front

Myocarditis after Pfizer mRNA vaccination is a rare event concentrated in adolescent and young adult males, with regulatory estimates of roughly 8 cases per million doses across ages 6 months–64 years and ~27 cases per million in males 12–24, while multiple observational studies and meta-analyses show SARS‑CoV‑2 infection carries a higher overall myocarditis risk across most age groups, particularly among males and young adults. Public health agencies and most systematic reviews conclude infection-related myocarditis risk exceeds vaccine‑associated risk, but a small set of recent analyses claims the opposite; these discrepancies reflect differences in methods, denominators, and time windows for follow‑up ^{[1] [2] [3] [4]}.

1. Why the headlines diverge — methods and denominators that change the story

Studies measuring myocarditis after vaccination often count events per million doses within a short post‑dose window (commonly seven days), while infection studies report events per infected persons over longer follow‑up (weeks to one year); those different denominators produce very different numerators and apparent risks. Regulatory summaries from the FDA and CDC use dose‑based incidence and short risk windows and identify the highest vaccine‑associated rates in adolescent and young adult males within a week of the second dose ^{[1] [2]}. By contrast, cohort and meta‑analytic research estimating myocarditis after SARS‑CoV‑2 infection aggregate events over months and report substantially higher incidence per infected person, with some studies showing several‑fold higher risk after infection than after vaccination ^{[5] [3]}. These methodological choices explain much of the apparent conflict between reports.

2. What U.S. regulators and vaccine manufacturers report — a concise portrait

U.S. authorities and Pfizer characterize vaccine‑linked myocarditis as rare and concentrated in young males. The FDA’s updated labeling cites approximately 8 cases per million doses overall (ages 6 months–64) and about 27 per million in males 12–24, reflecting post‑vaccination surveillance through 2025; Pfizer’s communications similarly emphasize rarity and the highest observed risk in males 12–17 ^{[1] [6]}. The CDC affirms a causal association between mRNA vaccines and myocarditis/pericarditis, especially within seven days of a second dose in adolescents and young adults, and continues to weigh those risks against benefits of preventing COVID‑19 and its cardiac complications ^[2]. Those official figures use conservative surveillance definitions and short risk windows designed to capture acute vaccine‑linked events.

3. What infection‑based studies show — higher myocarditis after COVID‑19

Multiple cohort studies and meta‑analyses find greater myocarditis risk after SARS‑CoV‑2 infection than after vaccination when comparing myocarditis per infected person to myocarditis per vaccinated dose or per person over longer follow‑up. A 2022 one‑year cohort found myocarditis incidence of 0.21 per 1,000 recovered patients within a year, and systematic reviews report infection‑associated myocarditis several times higher than vaccine‑associated myocarditis, with men and younger people disproportionately affected ^{[5] [3]}. Retrospective analyses also show elevated myocarditis rates after COVID‑19 compared with influenza and in young adults and males specifically ^[7]. These studies typically follow infected cohorts for months, capturing subacute and longer‑term cardiac sequelae that short post‑vaccine windows do not.

4. The outliers and why they matter — claims that vaccines are riskier

A minority of recent studies assert mRNA vaccines elevate myocarditis risk more than infection; one 2025 analysis reported markedly higher myocarditis associated with vaccines and contradicted many public‑health findings ^[4]. These outlier results underscore how study design, case ascertainment, background rates, and selection bias can flip conclusions: passive reporting systems, different diagnostic criteria, and failure to standardize denominators (doses versus infections versus person‑years) produce divergent risk estimates. Policymakers and clinicians must scrutinize these methodological choices because such studies can be amplified politically despite contradicting broader evidence synthesized by regulators and systematic reviews ^{[4] [3]}.

5. Bottom line for age groups and decision‑making — putting numbers in context

For adolescent and young adult males the relative vaccine‑associated myocarditis signal is strongest, yet absolute rates remain low (tens of cases per million doses), and the risk of myocarditis from SARS‑CoV‑2 infection is larger when measured per infected person over months, particularly in the same demographic groups. Public health recommendations balance these probabilities against the benefits of preventing COVID‑19, including hospitalizations and infection‑linked cardiac injury; hence regulators maintain vaccine use while warning and monitoring for myocarditis ^{[1] [2] [3]}. Clinicians should present both the short‑term vaccine risk and the longer‑term infection risk to patients, noting that methodological differences between studies drive much of the apparent disagreement.