[cthalupa]

It is a rare but known side effect of even regular flu vaccines causing myocarditis, e.g. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6786665/

>The true incidence of myocarditis after influenza vaccination may be underestimated because of the subclinical and nonspecific clinical manifestations of myocarditis. A prospective study about the incidence of cardiovascular adverse events after smallpox and influenza vaccination revealed that the rate of clinical or subclinical myocarditis and pericarditis after smallpox vaccination was approximately 1:5,500, despite the fact that the rate of troponin elevation was 1:200 [9]. Similarly, 2.6% of the influenza vaccine cohort showed new onset cardiac symptoms, such as chest pain, dyspnea, and palpitation, but no case of clinical or subclinical myocarditis and pericarditis