What are the absolute and relative myocarditis rates after mRNA COVID-19 vaccines vs after SARS-CoV-2 infection by age and sex?
Executive summary
Large population studies and regulator analyses show myocarditis after mRNA COVID‑19 vaccination is rare — typically single‑digit to low‑double‑digit cases per million doses overall, with highest risk concentrated in males 12–29 (estimates ~27 per million in males 12–24 for recent formulas) — while SARS‑CoV‑2 infection produces higher myocarditis risk overall and in young males in many studies (for unvaccinated men <40 infection added ~16 cases per million; some analyses show much larger excess after infection in some subgroups) [1] [2] [3] [4].
1. What the major reviews and regulators report — vaccinal risk is rare but concentrated in young men
Regulators and large reviews quantify vaccine‑associated myocarditis as uncommon but age‑ and sex‑specific: the FDA reported an unadjusted incidence of roughly 8 cases per million doses across ages 6 months–64 years for the 2023–24 mRNA formula and about 27 cases per million doses specifically in males 12–24 years [1]. Earlier syntheses and agency summaries put myocarditis after second mRNA doses around ~12.6 cases per million in 12–39‑year‑olds and note higher reporting after second doses in adolescent and young adult males [4] [5] [6]. Clinical consensus work estimated an incidence on the order of 0.95 per 100,000 (≈9.5 per million) overall and highlighted peak incidence in men aged 18–24 after two doses [7].
2. What large population studies found — infection risk often exceeds vaccine risk, but not uniformly
Population cohort and self‑controlled studies in England and elsewhere concluded myocarditis is more common after SARS‑CoV‑2 infection than after vaccination overall. The English self‑controlled case series (Patone et al.) found infection produced more myocarditis than vaccination overall, with infection adding roughly 16 excess myocarditis cases per million in unvaccinated men under 40 while vaccine doses produced smaller excesses except in specific vaccine/age/sex combinations [2] [3]. Other meta‑analyses and systematic reviews report that COVID‑19 survivors have a roughly two‑fold higher incidence of myocarditis over the following year compared with non‑infected controls [8].
3. Important subgroup nuance — Moderna (mRNA‑1273) second dose in young men stands out
The Patone analysis reported a striking finding: in men younger than 40, the number of excess myocarditis events per million was higher after a second dose of Moderna’s mRNA‑1273 (≈97 excess events per million) than after a positive SARS‑CoV‑2 test (≈16 excess events per million) during the study period [3]. That result signals a non‑uniform balance of risks across vaccine brands, doses, age and sex and underpins policy choices that favored different vaccine types or interval adjustments for younger males [3] [9].
4. Absolute versus relative framing — small absolute numbers, large relative increases in some comparisons
Many reports emphasize small absolute risks but measurable relative increases. For example, excess incidences above background have been estimated at about 1.2 per 100,000 for Pfizer and 1.9 per 100,000 for Moderna in some analyses — small absolute numbers that nevertheless represent a several‑fold increase over baseline in the affected groups [10]. By contrast, infection‑associated myocarditis in some studies is several times higher than vaccine‑associated myocarditis when measured with comparable methods [10] [8].
5. Clinical outcomes and prognosis — vaccine cases tend to have milder short‑term course in most cohorts
Clinical series and registry analyses report that myocarditis after mRNA vaccination has generally been treatable with favorable short‑term outcomes and lower incidence of adverse prognostic outcomes compared with viral myocarditis, though health‑care utilization sometimes remains similar and long‑term follow‑up data are still accruing [11]. That caveat matters for risk–benefit calculations: incidence is one input; severity and prognosis are another [11].
6. Limits, disagreements and evolving context
Available sources document disagreement across studies about magnitudes for specific age/sex/vaccine combinations. Some surveillance systems (VAERS) report lower crude rates for updated bivalent formulations versus original vaccines, while active‑surveillance cohort studies and international analyses show varied estimates depending on dose number, vaccine brand, age, sex and the comparator window used [12] [13] [4] [9]. Sources do not provide a single, complete table breaking out absolute and relative myocarditis rates by every age × sex × vaccine × infection scenario in one place; readers should treat point estimates as context‑dependent [1] [3].
7. Bottom line for readers and policymakers
The evidence in these sources is consistent that myocarditis is rare after mRNA vaccination but concentrated in young males and that, for most age/sex groups, SARS‑CoV‑2 infection confers equal or greater myocarditis risk than vaccination. Exceptions exist — notably higher excess after second doses of some mRNA products in young men [3] [1]. Policymakers and clinicians rely on both absolute numbers and prognosis: small increases in cases can warrant targeted policy changes (product choice, dosing intervals, booster recommendations) when concentrated in identifiable subgroups [1] [3] [6].
Sources: FDA labeling update and incidence estimates [1]; Circulation and literature reviews on vaccine myocarditis rates [4] [10]; English population study and subgroup findings (Patone et al.) reported in multiple repositories [3] [14] [15]; systematic review/meta‑analysis on post‑COVID myocarditis risk [8]; CDC clinical considerations [6].