What are estimated myocarditis incidence rates per million doses for Pfizer vs Moderna in recent large studies (2023-2025)?

1. Headlines: the blunt numbers regulators now use

The U.S. Food and Drug Administration required updated labeling stating that the estimated unadjusted incidence of myocarditis and/or pericarditis 1–7 days after the 2023–2024 mRNA formulations was approximately 8 cases per 1 million doses in people aged 6 months through 64 years and approximately 27 cases per 1 million doses in males 12–24 years; the agency’s language appears in FDA communications and summarized reporting ^{[1] [5]}. Several outlets restated the same 8 per million figure when reporting FDA actions in 2025 ^{[5] [6]}.

2. How head‑to‑head research frames Moderna vs Pfizer

Population studies and a JACC analysis repeatedly report that myocarditis risk after Moderna is higher—often two‑ to three‑fold—particularly after the second dose and in younger males; the 2–3× finding was highlighted in the JACC study and related reporting ^{[3] [7]}. A meta‑analysis pooling hundreds of millions of doses yielded a combined risk ratio of ~1.62 comparing Moderna to Pfizer, consistent with a modestly elevated risk with Moderna ^[4].

3. Absolute incidence varies by study design, age and dose

Surveillance systems, registry analyses and passive‑report datasets produce different absolute rates: Australian TGA summaries reported myocarditis roughly 1–2 per 100,000 (10–20 per million) for Pfizer and about 2 per 100,000 (20 per million) for Moderna in 2023 reports, numbers that mirror other jurisdictional safety reports but depend on reporting definitions and time windows ^{[8] [9] [10]}. Academic and clinical reviews present lower per‑dose reporting rates in some analyses (single‑digit per million in broad age ranges) and higher rates when restricted to young males or the week after dose two ^{[11] [1]}.

4. Where the ranges come from — methods matter

Different denominators and risk windows drive the spread of estimates. The FDA’s ~8 per million is an unadjusted 1–7 day incidence from commercial claims data for 2023–2024 formulations and aggregates ages 6 months–64 years ^[1]. TGA reporting used broader passive surveillance counts per doses administered up to mid‑2023 and expressed rates per 100,000 vaccinees ^[8]. Meta‑analyses and cohort studies that stratified by sex, age and dose show much higher rates specifically in males 12–24 after dose two versus very low rates in older adults ^{[4] [2] [3]}.

5. The most important caveat: subgroup concentration

All major sources emphasize that myocarditis risk is concentrated in adolescent and young adult males, and that absolute risk in older age groups is very low; the FDA language singles out males 12–24 with ~27 cases per million while broader populations show ~8 per million ^[1]. Studies comparing brands repeatedly find the Moderna‑associated increase is driven by these younger age groups ^{[3] [2]}.

6. Competing interpretations and remaining uncertainties

Researchers and regulators agree myocarditis after mRNA vaccines is rare, but disagreement exists on magnitude in narrow subgroups and on long‑term consequences. Some analyses and press pieces argue vaccine‑associated myocarditis is more common in certain cohorts and cite higher per‑million figures for Moderna in young men (p2_s5; ^[13] summaries cite very high subgroup numbers), while regulators and large surveillance syntheses present lower aggregated per‑dose estimates and emphasize rarity ^{[1] [4]}. Available sources do not mention long‑term outcome consensus beyond noting follow‑up and cardiac MRI studies are ongoing ^{[12] [1]}.

7. What readers should take away

For broad, population‑level comparisons from 2023–2025: expect roughly single‑digit to low‑teens myocarditis cases per million doses in general populations (regulatory aggregated estimate ~8/million), with Moderna showing a reproducible 1.6–3× higher rate than Pfizer in younger males and the highest subgroup estimates around a few dozen cases per million in males aged about 12–24 ^{[1] [4] [3]}. Different studies use different windows, age strata and surveillance systems; those methodological choices explain most of the variation in quoted “per million” numbers ^{[1] [8] [4]}.

Limitations: this summary uses available regulatory statements, cohort comparisons and meta‑analyses in the provided set; available sources do not mention every single large study from 2023–2025 and do not provide a single harmonized, age‑specific rate table across studies ^{[4] [1]}.