Clinical outcomes of myocarditis after SARS-CoV-2 mRNA vaccination in four Nordic countries: population based cohort study
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  • Published on:
    Providing comments on methods, analyses & conclusions. Seeking additional information & response from the authors.

    I read with interest the Nordic myocarditis cohort study by Husby et al (1) on clinical outcomes of three different types of myocarditis: COVID-19 mRNA vaccination-associated (“vaccine-associated”), COVID-19 infection-associated (“infection-associated”) and “conventional” myocarditis. I would like to make several comments and request response from the authors.

    A significant limitation of the Nordic and other similar studies is the under-diagnosis of COVID-19 vaccine-associated myocarditis and possibly COVID-19 infection-associated myocarditis. To be included in the Nordic myocarditis cohort study, an individual had to develop symptom(s) with myocarditis, present to a medical provider with such symptom(s), and the medical provider had to consider myocarditis and then order at least ECG or cardiac enzyme(s), and the individual had to be admitted to the hospital as an inpatient. Individuals with myocarditis who did not satisfy all the above conditions would not have been included in the Nordic study. Only a prospective study with continuous screening for myocardial injury/inflammation would be able to provide complete information on the incidence and outcomes of myocarditis associated with COVID-19 vaccine or infection. Limited prospective data on myocardial injury post-vaccine is currently available, suggesting significantly more common occurrence (2,3) than proclaimed but with unknown long-term prognosis.

    During the COVID-19 pandemic, there were many more pat...

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    Conflict of Interest:
    None declared.
  • Published on:
    Seeking more information on risk factors and vaccination status of those w/myocarditis post-SARS-CoV-2
    • Tracy Beth Høeg, MD, PhD Physician Epidemiologist Department of Epidemiology and Biostatistics, University of California-San Francisco
    • Other Contributors:
      • Miloš Miljković, MD, Chief Medical Officer
      • Vinay Prasad, MD, MPH Professor of Epidemiology and Biostatistics

    To the Editor:

    We read with interest the Nordic registry study by Husby et al on clinical outcomes of three different types of myocarditis: SARS-CoV-2 mRNA vaccination-associated, COVID-19 associated and “conventional” myocarditis. We appreciate the information the authors provided on patient characteristics by myocarditis type. We note >50% patients with COVID-19-associated and conventional myocarditis were over 40, those with vaccine-associated myocarditis were younger on average and 38% were 12-24 years v.s <25% for the other two types. Further, the proportion of men was higher in all three categories, and the proportion of patients with underlying comorbidities similar; however, we wonder, given the relatively small number of patients, if the authors could disclose which comorbidities and how many were present (in total) among the patients with COVID-19 vs. vaccination-associated myocarditis, perhaps as a summary table.

    Second, do the authors have any information on the vaccination status (number of doses and dates given in relation to the myocarditis diagnosis) among those categorized as having COVID-associated myocarditis? If so, could this information be broken down by age group?
    Related, the most recent exposure defined the type of myocarditis in patients who received both an mRNA vaccine and had a positive test for SARS-CoV-2 in the last 28 days. We therefore wonder if the authors could provide the number of times both were diagnosed with...

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    Conflict of Interest:
    None declared.