So does the small pox vaccine but its not an MRNA vaccine. The reaction is not the vaccine its the immune response to the invader. As a science translator this is the best explanation I can give: Although the long-term outcomes of vaccine-associated myocarditis and pericarditis are unclear, the current knowledge on the short-term clinical trajectories are reassuring. The clinical presentations of myocarditis after COVID-19 mRNA vaccination have been predominantly mild and few patients have required intensive treatment.

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 However, one case-series, published in 2022, of adolescent patients found a persistence of radiographic abnormalities at follow-up examinations, which could be cause for concern.

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 However, the patients followed up had excellent clinical outcomes, suggesting minimal chronic morbidity attributable to vaccine-associated myocarditis. Nevertheless, the continuous surveillance of this patient group for any increased frequency of heart failure, sudden death, or related cardiac comorbidities is necessary.

With regard to the underlying disease mechanism, it is necessary to note that myocarditis and pericarditis are not novel side-effects of vaccination. Other vaccinations, especially smallpox vaccination, have previously been associated with a similar increased risk of myocarditis.

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 These findings suggest that the disease mechanism is specific neither to the newly developed mRNA vaccines nor to exposure to the SARS-CoV-2 spike protein. Other mechanisms have been suggested, yet hard evidence explaining the association is absent. Future mechanistic studies into potential mechanisms are therefore warranted and could provide valuable insight, leading to even safer COVID-19 mRNA vaccines.