Which mRNA vaccine (Pfizer vs Moderna) shows higher myocarditis risk by age and sex, and how does that compare to infection risk?

1. Who bears the highest vaccine-associated myocarditis risk — age and sex pattern

Regulatory agencies and summaries consistently identify young males (roughly ages 12–24) as having the highest observed myocarditis risk after mRNA doses; the FDA and CDC materials say the observed risk was highest in males 12–24 years of age ^{[6] [7]}. Published safety syntheses and country reports quantify that pattern: passive and active surveillance in several countries found markedly elevated reporting or hospitalization rates in males under 30 after the second dose, with multiple sources showing the largest excess after dose two ^{[2] [1]}.

2. Moderna vs Pfizer — which vaccine shows higher myocarditis rates, and by how much

Multiple pharmaco‑epidemiologic studies and clinical reviews find higher myocarditis incidence after Moderna (mRNA‑1273/Spikevax) than Pfizer (BNT162b2/Comirnaty) in younger males. For example, an American analysis cited by the American Heart Association reported Moderna produced a larger excess of myocarditis cases in men under 40 — an additional 97 cases per million after a second Moderna dose compared with smaller Pfizer excesses in similar analyses ^[1]. A clinical consensus review compiled international figures showing second‑dose reporting rates for 18–29 year‑olds of about 140 per million for Moderna versus 25 per million for Pfizer in Canadian passive surveillance, and self‑controlled analyses with Moderna rates many times higher than Pfizer in males <40 ^[2]. These numbers indicate Moderna’s myocarditis signal is substantially larger in young males across multiple datasets ^[2].

3. How vaccine risk compares with myocarditis after infection

Several large‑scale studies and meta‑analyses find the risk of myocarditis from SARS‑CoV‑2 infection is greater than the risk after vaccination in most age groups. A systematic review found roughly 0.21 myocarditis cases per 1,000 COVID survivors vs 0.09 per 1,000 controls over ~9.5 months ^[5]. Population studies in children and young people in England estimated infection caused 2.24 extra myocarditis/pericarditis cases per 100,000 over six months versus 0.85 extra cases per 100,000 among vaccinated cohorts — the authors and outlets concluded infection posed higher and longer‑lasting risk than vaccination ^{[3] [4]}. The American Heart Association likewise summarized that infection‑associated myocarditis risk was higher than vaccine‑associated risk in reviewed data ^[1].

4. Limitations, disagreements and methodological caveats

Studies use different designs (passive reporting, self‑controlled case series, cohort linkage), time windows (14–30 days after dose vs months after infection), and denominators (hospitalized cases vs reports), producing heterogeneous rate estimates ^{[2] [7]}. Passive surveillance (e.g., VAERS, CARFISS) can over‑ or under‑estimate incidence and cannot prove causation without context ^{[8] [2]}. Some commentators dispute interpretation of specific studies (e.g., critiques of UK analyses arguing data omissions or adjustment choices), showing there is debate about absolute magnitudes in children and teens ^[9]. FDA actions to expand labeling reflect evolving evidence and different risk thresholds across regulators ^{[6] [10]}.

5. Practical implications for individuals and policy

Public health agencies balance rare vaccine harms against broader benefits: reduced hospitalizations, severe COVID, and myocarditis risk from infection. FDA and product labels now explicitly warn about myocarditis/pericarditis risk and note the highest observed rates in young males, informing clinicians and vaccinees ^[6]. Moderna’s higher observed myocarditis signal in young males has prompted age‑targeted communications and risk‑mitigation considerations in some jurisdictions ^{[2] [10]}.

6. What the current sources do not settle

Available sources do not mention long‑term comparative outcomes (beyond short‑to‑medium follow‑up) for vaccine‑associated versus infection‑associated myocarditis in all age strata; nor do they provide a single unified incidence table directly comparing Moderna vs Pfizer by each single year of age and sex using identical methodology — differences in study design and population mean exact, directly comparable per‑age numbers are not uniformly available in the cited material ^{[2] [5] [3]}.

Bottom line: Young males face the highest vaccine‑associated myocarditis rates, and multiple data syntheses show Moderna carries a larger myocarditis signal than Pfizer in that demographic; however, infection with SARS‑CoV‑2 generally confers a higher myocarditis risk than vaccination in population studies — interpretation of absolute magnitudes depends on study choice, surveillance system, and follow‑up window ^{[2] [1] [3]}.