The discovery of the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) in December 2019 led to an urgent global focus on developing vaccines to combat the spread and severity of COVID-19. The Pfizer-BioNTech COVID-19 vaccine was granted emergency use authorization by the US Food and Drug Administration (FDA) on December 11, 2020, followed by Moderna and Janssen/Johnson & Johnson vaccines. As of April 2022, over 11.5 billion COVID-19 vaccine doses have been administered worldwide.
Vaccine Side Effects:
While most side effects of COVID-19 vaccines are mild and self-limited, serious side effects have been reported, including myocarditis. This review explores the current literature on myocarditis following COVID-19 vaccination, covering aspects such as incidence, risk factors, clinical presentation, imaging findings, pathophysiologic mechanisms, treatment, and prognosis.
Definition and Incidence:
Myocarditis associated with vaccination is defined based on a close temporal relationship between vaccine administration and symptom onset, usually within 14 days. The Vaccine Adverse Events Reporting System (VAERS) in the US has received reports of myocarditis and pericarditis following COVID-19 vaccination, with an incidence of 18 per million vaccine doses globally. Rates vary by age and sex, with the highest risk observed in men aged 12 to 29 years, particularly after the second dose.
Sex and Age Differences:
Reports show a higher incidence of myocarditis in young men, raising questions about potential underdiagnosis in women. Incidence is lower in younger children and adults over 30 years. Among mRNA-based vaccines, Moderna has a higher risk compared to Pfizer-BioNTech, with the second dose carrying a greater risk. Limited data on third and subsequent booster doses suggest a lower risk than the second dose.
Risk Relative to COVID-19 Infection:
Comparatively, the risk of myocarditis after vaccination is much lower than the risk associated with SARS-CoV-2 infection. Studies indicate a higher risk of myocarditis after infection than after vaccination, emphasizing the importance of considering the overall risk-benefit balance.
Clinical Presentation:
Myocarditis following vaccination presents with symptoms like chest pain, fever, chills, and myalgias. Most cases occur within the first week post-vaccination, with chest pain being the most common presenting symptom.
Histopathology and Pathophysiology:
Histologically, lymphocytic myocarditis is predominant, often presenting as a fulminant, potentially fatal disease in rare instances. Proposed mechanisms include molecular mimicry, direct binding of viral spike glycoprotein to cardiomyocytes, and innate inflammatory responses to the mRNA-encoded viral spike glycoprotein.
Role of Cardiac Imaging:
Cardiac imaging, particularly cardiac magnetic resonance imaging (CMR), plays a crucial role in diagnosing myocarditis. CMR findings in vaccine-associated myocarditis are similar to other causes but tend to be milder. Follow-up CMR data suggest resolution of edema and normalization of left ventricular function, with minimal residual fibrosis.
Other Investigations and Management:
Electrocardiography and cardiac biomarkers aid in diagnosis, while management is primarily supportive, addressing potential complications such as heart failure or arrhythmias. Patients with mild symptoms typically experience a transient, mild course with complete resolution within 1 to 3 weeks.
Clinical Course and Adverse Outcomes:
Most cases of myocarditis following COVID-19 vaccination have a mild course, with short hospital stays, if required. Long-term follow-up data are limited, emphasizing the need for further research on the risk associated with subsequent vaccine doses and other potential risk factors.
Conclusion:
While myocarditis following COVID-19 vaccination is a rare occurrence, understanding its incidence, risk factors, and clinical course is crucial for informed decision-making. Ongoing research is necessary to evaluate long-term outcomes and potential risks associated with additional vaccine doses. As with any medical condition, individuals are encouraged to consult with healthcare professionals to make informed choices about vaccination based on their unique health circumstances.
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