Prognosis of COVID-19 Vaccine Myocarditis Compared With Viral Myocarditis
- This is a retrospective study comparing the outcomes of myocarditis post–BNT162b2 vaccination to that of viral infection–related myocarditis using a public health care database in Hong Kong.
- Vaccine-related myocarditis was rare (2.61 per 100,000 vaccinations) and was associated with lower risk of death compared to viral infection–related myocarditis.
- The study is limited by the use of ICD codes, small number of cases, and its inclusion of only BNT162b2 vaccinations.
How do outcomes of myocarditis post–severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccination compare with that of viral infection–related myocarditis?
This is a retrospective cohort study of a public health care database in Hong Kong, utilizing data spanning from March 6, 2021, the day of roll-out of the BNT162b2 (Pfizer–BioNTech) mRNA SARS-CoV-2 vaccine, up to March 31, 2022, to identify all patients ages ≥12 years diagnosed with myocarditis within 28 days after receiving any dose of the vaccine. For the comparison cohort, data from January 1, 2000–December 21, 2019 were examined to identify patients ages ≥12 years with a diagnosis of viral infection–related myocarditis. Cases without an elevated troponin were excluded. Several outcomes were examined: death, heart failure, dilated cardiomyopathy, heart transplant, intensive care unit (ICU) admission, and rehospitalization. All diagnoses and outcomes were based on International Classification of Diseases (ICD) codes. Follow-up was 180 days post-event, the end of data availability, or March 31, 2022.
Of close to 9 million BNT162b2 doses administered in 4 million individuals, 104 cases of myocarditis within 28 days of vaccination were identified after applying exclusion criteria. In the comparator cohort, 762 cases of viral infection–related myocarditis were identified. The incidence of myocarditis following vaccination was 2.61 (95% confidence interval [CI], 2.14-3.17) per 100,000 vaccinations. These patients were more likely male, and most (65.4%) had received the second dose. Over the follow-up period, 1 death out of 104 (1.0%) patients with post-vaccination myocarditis and 84 deaths (11.0%) out of 762 patients with viral infection–related myocarditis were identified, respectively. One case (1.0%) of dilated cardiomyopathy and two cases (1.9%) of heart failure were identified in the post-vaccination group, compared with 28 (3.7%) and 93 (12.2%) in the viral infection–related myocarditis group, respectively. Adjusted analysis showed that the post-vaccination myocarditis group had a 92% lower mortality risk (adjusted hazard ratio, 0.08; 95% CI, 0.01-0.57). No significant differences in other prognostic outcomes were seen.
Mortality of SARS-CoV-2 vaccine-related myocarditis is significantly lower than viral infection–related myocarditis.
The value of this study is in its comparing outcomes of SARS-CoV-2 vaccine-related myocarditis to viral infection–related myocarditis. Estimates in this study were comparable to previously reported population-based cohorts, lending validity to the findings. Of note, this study includes only patients who have received the BNT162b2 mRNA vaccine; thus, the data cannot be directly extrapolated to other vaccines. Other limitations include the reliance of ICD codes for diagnosis, clinical characteristics, and outcomes, in addition to the small number of cases in both groups. Nevertheless, these data are reassuring, and in line with impressions that the consequences of vaccine-related myocarditis are much less dire than viral infection–related cases.
Clinical Topics: Cardiac Surgery, COVID-19 Hub, Heart Failure and Cardiomyopathies, Invasive Cardiovascular Angiography and Intervention, Prevention, Cardiac Surgery and Arrhythmias, Cardiac Surgery and Heart Failure, Acute Heart Failure, Heart Transplant
Keywords: Cardiomyopathy, Dilated, COVID-19, COVID-19 Vaccines, Heart Failure, Heart Transplantation, Intensive Care Units, Myocarditis, Primary Prevention, RNA, Messenger, SARS-CoV-2, Troponin, Vaccination
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