According to this review article, there are multiple ways by which an mRNA vaccine cause myocarditis. The exact mechanism has not been elucidated and probable there is more than one reason at the same time.
These are the proposed mechanisms:
- Molecular mimicry between the spike protein of SARS-CoV-2 and heart tissue-associated self-antigens.
- Immune response to mRNA.
- Trigger of preexisting dysregulated immune pathways (including a dysregulated cytokine expression).
It is important to note that there is a predominance in young male with respect to females in general. The presence or absence of testosterone may provide an environment that can make someone more or less susceptible to myocarditis .