Prognosis of Myocarditis Developing After mRNA COVID-19 Vaccination Compared With Viral Myocarditis.

Background: Association between messenger RNA (mRNA) COVID-19 vaccines and myocarditis has aroused public concern over vaccine safety.
Objectives: The goal of this study was to compare the prognosis of this condition with viral infection-related myocarditis over 180 days.
Methods: A territory-wide electronic public health care database in Hong Kong linked with population-based vaccination records was used to conduct a retrospective cohort study. Since the roll-out of BNT162b2 (Pfizer-BioNTech), patients aged ≥12 years hospitalized with myocarditis within 28 days after BNT162b2 vaccination were compared against viral infection-related myocarditis recorded before the pandemic (2000-2019), over a 180-day follow-up period (starting from diagnosis of myocarditis). All-cause mortality, heart failure, dilated cardiomyopathy, heart transplant, and postdischarge health care utilization were examined with Cox proportional hazards models.
Results: A total of 866 patients were included for analysis. Over the follow-up period, 1 death (1.0%) of 104 patients with postvaccination myocarditis and 84 deaths (11.0%) of 762 patients with viral infection-related myocarditis were identified. One case (1.0%) of dilated cardiomyopathy and 2 cases (1.9%) of heart failure were identified in the postvaccination group, compared with 28 (3.7%) and 93 (12.2%) in the viral infection-related myocarditis group, respectively. Adjusted analysis showed that the postvaccination myocarditis group had a 92% lower mortality risk (adjusted HR: 0.08; 95% CI: 0.01-0.57). No significant differences in other prognostic outcomes were seen.
Conclusions: This study found a significantly lower rate of mortality among individuals with myocarditis after mRNA vaccination compared with those with viral infection-related myocarditis. Prognosis of this iatrogenic condition may be less severe than naturally acquired viral infection-related myocarditis.
Competing Interests: Funding Support and Author Disclosures This study was funded by a research grant from the Food and Health Bureau, the Government of the Hong Kong Special Administrative Region (reference COVID19F01). Drs Lai and I.C. Wong are partially supported by the Laboratory of Data Discovery for Health (D(2)4H) funded by AIR@InnoHK administered by the Innovation and Technology Commission. Dr Lai has been supported by the RGC Postdoctoral Fellowship under the Hong Kong Research Grants Council; and has received research grants from the Food and Health Bureau of the Government of the Hong Kong Special Administrative Region, outside the submitted work. Dr Chui has received grants from the Food and Health Bureau of the Government of the Hong Kong Special Administrative Region, Hong Kong Research Grant Council, Hong Kong Innovation and Technology Commission, Pfizer, IQVIA, and Amgen; and has received personal fees from PrimeVigilance, outside the submitted work. Dr Li has received research grants from the Food and Health Bureau of the Government of the Hong Kong Special Administrative Region; has received research and educational grants from Janssen and Pfizer; has received internal funding from the University of Hong Kong; and has received consultancy fees from Merck Sharp & Dohme, unrelated to this work. Dr Wan has received research grants from the Food and Health Bureau of the Government of the Hong Kong Special Administrative Region, and the Hong Kong Research Grants Council, outside the submitted work. Dr Chan has received honorarium from the Hospital Authority; and has received grants from the Hong Kong Research Grants Council, Research Fund Secretariat of the Food and Health Bureau, National Natural Science Fund of China, Wellcome Trust, Bayer, Bristol Myers Squibb, Pfizer, Janssen, Amgen, Takeda, and Narcotics Division of the Security Bureau of the Hong Kong Special Administrative Region, outside the submitted work. Dr Wong has received research funding outside the submitted work from Amgen, Bristol Myers Squibb, Pfizer, Janssen, Bayer, GSK, Novartis, the Hong Kong Research Grants Council, the Food and Health Bureau of the Government of the Hong Kong Special Administrative Region, National Institute for Health Research in England, European Commission, and the National Health and Medical Research Council in Australia; has received speaker fees from Janssen and Medice in the previous 3 years; and is an independent non-executive director of Jacobson Medical in Hong Kong. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose.
(Copyright © 2022 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.)