What are the rates of serious post-vaccine adverse events (myocarditis, VTE, Guillain-Barré) by age, sex, and comorbidity?
Executive summary
Available studies show myocarditis after mRNA COVID-19 vaccines is rare but concentrated in adolescent and young adult males (excess risk up to ~20 per 100,000 doses in some groups), venous thromboembolism (VTE) signals are small or inconsistent and strongly age-related, and Guillain–Barré syndrome (GBS) risks are low overall but appear higher after some adenoviral‑vector vaccines (e.g., ChAdOx1/Vaxzevria and Ad26.COV2.S) than after mRNA vaccines [1] [2] [3] [4] [5]. Coverage across sources varies by outcome, and comorbidity‑specific, sex‑and‑age‑stratified rates are reported unevenly [1] [6] [4].
1. Myocarditis: concentrated risk in young males after mRNA doses
Multiple population and systematic studies agree that myocarditis/pericarditis after COVID‑19 vaccination is uncommon but not uniform: the highest attributable risks are after mRNA vaccines in adolescent and young adult males, especially after the second dose; estimates include about 10.18 excess cases per 100,000 doses in boys 12–17 for BNT162b2 and up to ~20 per 100,000 in men 18–24 for mRNA‑1273 in pooled analyses [1]. Large cohort/self‑controlled analyses also show the vaccine‑associated myocarditis risk is concentrated in males <40 and is smaller than the myocarditis risk following SARS‑CoV‑2 infection for most age/sex groups [7] [8]. Clinical summaries from CDC/medical societies note cases are usually short‑term and most patients improve, and they emphasize that vaccination benefits still outweigh risks for most groups [2] [9].
2. Age, sex and dose matter — granular myocarditis numbers where available
Systematic reviews and active‑surveillance studies present dose‑ and age‑stratified estimates: for example, analyses that parsed by dose found the second mRNA dose produced the highest excess case counts in teenage boys and young men; rates vary by vaccine product (higher with some mRNA products in some studies) and by dose interval [1] [10]. However, not every source gives a full table of rates by every age/sex/comorbidity cell; many rely on pooled excess‑case or per‑dose estimates rather than complete cross‑tabulations [1] [11].
3. Venous thromboembolism (VTE): background rates large, vaccine signals small or mixed
VTE is primarily an age‑related event: population incidence rises strongly with age and varies by sex and comorbidity (background ≈71–117 per 100,000/year in many studies, and much higher in older adults) [12] [6]. Analyses of vaccinated cohorts—such as older U.S. veterans—found only minimal absolute increases in VTE after COVID‑19 vaccination (adjusted 60‑day VTE rates ≈1.375 per 1,000 in vaccinated vs 1.374 per 1,000 in controls; tiny absolute differences) [3]. Observational literature warns that background VTE risks differ markedly by age, sex and comorbidities (e.g., cancer, obesity) and that comparisons must adjust for these factors [6] [13] [14].
4. Guillain–Barré syndrome: low background incidence; higher signals with some adenoviral vaccines
GBS has a low background rate (roughly 1–2 per 100,000 person‑years) and most surveillance work finds little or no increase after mRNA vaccines [15] [16]. Cohort and multinational self‑controlled studies identified increased relative incidence of GBS after certain adenoviral‑vector vaccines (for example, ChAdOx1‑S/Vaxzevria showed RI ≈3.10 in one multinational analysis) and the U.S. Vaccine Safety Datalink flagged an association with Ad26.COV2.S, leading to warnings and separate monitoring [4] [5]. Case reports and case‑series analyses exist but cannot produce population rates without denominators; systematic reviews stress the difference between temporal reports and established causality except where repeated analytical studies show consistent elevation [17] [18].
5. Comorbidities and sex: uneven reporting and important caveats
Sources repeatedly note that comorbidities (e.g., prior cardiac disease, obesity, cancer, age‑related frailty) change baseline risk substantially, and many vaccine‑safety analyses adjust for comorbidity indices only incompletely or present pooled results [19] [3] [20]. For myocarditis, most datasets report sparse comorbidity stratification beyond age and sex [11]. For VTE and GBS, older age and classic VTE/GBS risk factors dominate event risk; some studies show specific comorbidities (e.g., coronary artery disease) increase hospitalization for adverse events but comprehensive comorbidity-by‑sex‑by‑age rate tables are generally not provided in the reviewed literature [3] [21].
6. What reporting systems and study types tell—and don’t tell—you
Passive surveillance (VAERS) captures signals but cannot prove causation or accurate rates without active‑surveillance denominators; agencies combine VAERS with active systems (VSD, BEST, EudraVigilance) to estimate age/sex/dose risks [22] [23]. Systematic reviews and self‑controlled cohort designs provide stronger, age/sex‑stratified risk estimates for myocarditis and GBS linked to vector vaccines; for VTE the strongest signals are that absolute vaccine‑associated increases are small compared with background and with the risks from COVID‑19 infection itself [8] [3] [5].
Limitations: the reviewed sources do not provide a single, fully cross‑tabulated table of myocarditis, VTE and GBS rates by every age×sex×comorbidity cell; available reports vary in vaccine types, time windows, and methods [1] [24] [5]. If you want, I can extract specific numeric estimates (per‑dose or per‑person‑year) from any one of the cited studies and present a side‑by‑side age/sex table drawn only from that source.