Clinical outcomes of myocarditis after SARS-CoV-2 mRNA vaccination in four Nordic countries: population based cohort study

Abstract

ObjectiveTo investigate the clinical outcomes of myocarditis associated with mRNA vaccines against the SARS-CoV-2 virus compared with other types of myocarditis.DesignPopulation based cohort study.SettingNationwide register data from four Nordic countries (Denmark, Finland, Norway, and Sweden), from 1 January 2018 to the latest date of follow-up in 2022.ParticipantsThe Nordic myocarditis cohort; 7292 individuals aged ≥12 years who had an incident diagnosis of myocarditis as a main or secondary diagnosis, in a population of 23 million individuals in Denmark, Finland, Norway, and Sweden.Main outcome measuresHeart failure, or death from any cause within 90 days of admission to hospital for new onset myocarditis, and hospital readmission within 90 days of discharge to hospital for new onset myocarditis. Clinical outcomes of myocarditis associated with SARS-CoV-2 mRNA vaccination, covid-19 disease, and conventional myocarditis were compared.ResultsIn 2018-22, 7292 patients were admitted to hospital with new onset myocarditis, with 530 (7.3%) categorised as having myocarditis associated with SARS-CoV-2 mRNA vaccination, 109 (1.5%) with myocarditis associated with covid-19 disease, and 6653 (91.2%) with conventional myocarditis. At the 90 day follow-up, 62, nine, and 988 patients had been readmitted to hospital in each group (vaccination, covid-19, and conventional myocarditis groups, respectively), corresponding to a relative risk of readmission of 0.79 (95% confidence interval 0.62 to 1.00) and 0.55 (0.30 to 1.04) for the vaccination type and covid-19 type myocarditis groups, respectively, compared with the conventional myocarditis group. At the 90 day follow-up, 27, 18, and 616 patients had a diagnosis of heart failure or died in the vaccination type, covid-19 type, and conventional myocarditis groups, respectively. The relative risk of heart failure within 90 days was 0.56 (95% confidence interval 0.37 to 0.85) and 1.48 (0.86 to 2.54) for myocarditis associated with vaccination and covid-19 disease, respectively, compared with conventional myocarditis; the relative risk of death was 0.48 (0.21 to 1.09) and 2.35 (1.06 to 5.19), respectively. Among patients aged 12-39 years with no predisposing comorbidities, the relative risk of heart failure or death was markedly higher for myocarditis associated with covid-19 disease than for myocarditis associated with vaccination (relative risk 5.78, 1.84 to 18.20).ConclusionsCompared with myocarditis associated with covid-19 disease and conventional myocarditis, myocarditis after vaccination with SARS-CoV-2 mRNA vaccines was associated with better clinical outcomes within 90 days of admission to hospital.

COVID-19 vaccination was a rare potential etiology for cause of death after medicolegal autopsy. A Finnish nationwide study

“…A link between myocarditis and mRNA-type COVID-19 vaccines has been established in large cohort studies (10–11). The highest risk for developing myocarditis has occurred in young men after receiving the second dose (50) Case reports of vaccination-associated myocarditis deaths have been published (35, 51), but, in large study settings, post vaccination myocarditis has rarely been associated with death (8, 10, 13, 50, 52). Notably, myocardial injury associated with a clinical diagnosis of myocarditis after COVID-19 vaccination has been reported mild, as reviewed by Garg et al (53).…”

“…However, though myocarditis is a severe condition, reports in young men show relatively mild outcomes and no mortality associated with myocarditis shortly after vaccination (11)(12). Furthermore, based on a population-based follow-up study of vaccine-related myocarditis, deaths are very rare (13).…”

Adverse Events Following SARS-CoV-2 mRNA Vaccination in Adolescents: A Norwegian Nationwide Register-Based Study

“…Other studies reporting increased post-vaccination myocarditis risk similarly report no vaccine-arrhythmia association,[10, 27, 42] while a Malaysian study report increased risk. [30] Post-vaccination myocarditis might be milder,[40, 43] resulting in fewer arrhythmias, or arrhythmias might be less common in adolescents.…”

Diagnosis of Acute Myocarditis Following mRNA Vaccines against SARS-CoV-2: A Methodological Review

“…Some disparities were also noted; indeed, young males, especially after the second vaccination dose, seemed to be the group at higher risk [18]. However, the reported risk of myocarditis markedly varies according to the analyzed population and the associated previous medical history [19][20][21][22]. Probably, young subjects are more prone to develop acute myocarditis after SARS-CoV-2 immunization because of a hyperimmune response; in fact, young individuals have a stronger immune response compared with older ones [23].…”