Myocarditis After Viral Illness and After Vaccination: Distinguishing the Two in a Sceptical Consultation
DOI:
https://doi.org/10.5281/zenodo.22497101Keywords:
Myocarditis, COVID-19 vaccines, mRNA vaccines, Risk communication, Vaccine hesitancy, PharmacovigilanceAbstract
Myocarditis can follow either a viral illness or an mRNA COVID-19 vaccine dose, and both possibilities now regularly arise
in the same clinic visit. This review sets the incidence and prognosis data for each side by side. A Nordic cohort of 23.1 million
residents found an adjusted incidence rate ratio for myocarditis after a second mRNA-1273 dose of 6.57 (95% CI 4.64-9.28)
overall and 13.83 (8.08-23.68) in men aged 16-24, versus 1.75 (1.43-2.14) and 5.31 (3.68-7.68) respectively for BNT162b2. A
US PCORnet analysis of over 45 million patients found cardiac complications consistently more common after SARS-CoV-2
infection than after vaccination in every age and sex stratum studied: in men aged 18-29, 63.7 cases per 100,000 after
infection versus 8.4 per 100,000 after a second dose. A self-controlled case series in 50 million people in England found 10.2
excess myocarditis/pericarditis cases per million after infection in 16-39-year-olds, rising to 18.1 per million in adults 40 and
older, against 3.5 to 4.5 excess cases per million after a booster dose in the younger group. Prognosis also differs: in a Hong
Kong cohort of 104 post-vaccination and 762 viral myocarditis cases, six-month mortality was 1.0% versus 11.0% (adjusted
hazard ratio 0.1), and heart failure developed in 1.9% versus 12.2%. These are genuinely different risk-benefit pictures, not
two versions of the same story, and a clinician facing a sceptical patient needs absolute numbers, not slogans, to represent
either fairly. This review sets out those numbers and a practical, non-dismissive approach to the consultation in which they
come up.
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