Recent studies and analyses have raised concerns about adverse effects associated with COVID-19 mRNA vaccines, particularly those produced by Pfizer and Moderna. Research published on SSRN and PubMed highlights serious adverse events such as myocarditis, pericarditis, and severe aplastic anemia following mRNA vaccination. A Korean nationwide study specifically examined COVID-19 vaccination-related myocarditis. Autopsy findings from cases of fatal vaccine-induced myocarditis have been documented, with some researchers linking myocarditis directly to cardiac arrest and sudden death. Genetic research indicates that mRNA vaccines may cause disruption of thousands of genes, potentially leading to mitochondrial failure, cancer, and immune dysfunction. A notable case involved the detection of Pfizer vaccine DNA in a colon cancer biopsy of a quadruple-vaccinated patient, where replication-competent vaccine DNA producing spike proteins was found, and the patient subsequently died. A systematic review and meta-analysis published in BMJ Open assessed the risk of myocarditis and pericarditis in vaccinated versus unvaccinated populations. Critics emphasize the lack of prospective, double-blind, randomized, placebo-controlled trials to conclusively establish vaccine safety, suggesting that the risks of myocarditis may outweigh the theoretical benefits of vaccination.