LogFAQs > #971803678

https://www.ncbi.nlm.nih.gov/books/NBK459259/#article-25470.s4

The incidence of myocarditis is approximately 1.5 million cases worldwide per year. Incidence is usually estimated between 10 to 20 cases per 100,000 persons. The overall incidence is unknown and probably underdiagnosed.

So the Covid vaccine accounted for an extra 5-10% more cases. It might actually be less than that, but where other instances are often underdiagnosed because the symptoms aren't severe enough to warrant a doctor visit and/or meet the clinical threshold, I'm inclined to assume that roughly the same pattern applies to vaccine-induced cases and that vaccine-induced myocarditis is equally underdiagnosed. That's speculation and I don't have any concrete basis for that opinion, but intuitively it makes sense.