Clinical Presentation and Outcomes of Myocarditis Post mRNA Vaccination: A Meta-Analysis and Systematic Review

Abstract
Background: Myocarditis is being increasingly reported as a potential complication of both Pfizer-BioNTech and Moderna vaccines for COVID-19. One thousand five hundred and twenty-two cases were reported as of September 02, 2021, as per CDC’s (Centers for Disease Control) vaccine adverse event reporting system. Most of the published data is available in the form of case reports and series. There is a need to compile the demographic data, clinical features, and outcomes in these patients.

Methods: A systematic search was conducted in PubMed, Embase, Web of science, and google scholar for published literature between January 01, 2020, and July 17, 2021. Individual data of 69 patients were pooled from 25 qualifying case reports and case series.

Results: The median age of onset was 21 years. 92.7% of the patients were male. 76.8% of patients received the Pfizer-BioNTech vaccine, and 23.2% received the Moderna vaccine. 88.5% developed symptoms after the second dose. Patients were admitted to the hospital a median of three days post-vaccination. All the patients had chest pain and elevated troponin. The myocarditis was confirmed on cardiac MRI in 87% of the patients. Most of the patients had late gadolinium enhancement on MRI. The median length of stay was four days. All the reported patients recovered and were discharged.

Conclusion: Post-mRNA vaccination myocarditis is seen predominantly in young males within a few days after their second dose of vaccination. The pathophysiology of myocarditis is not well known. The prognosis is good as all the reported patients recovered. The presence of late gadolinium enhancement on cardiac MRI indicated myocardial necrosis/fibrosis and further studies are needed to establish the long-term prognosis of the condition.

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