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Myocarditis Cases Reported After mRNA-Based COVID-19 Vaccination in the US From December 2020 to August 2021

Educational Objective
To identify the key insights or developments described in this article
Key Points

Question  What is the risk of myocarditis after mRNA-based COVID-19 vaccination in the US?

Findings  In this descriptive study of 1626 cases of myocarditis in a national passive reporting system, the crude reporting rates within 7 days after vaccination exceeded the expected rates across multiple age and sex strata. The rates of myocarditis cases were highest after the second vaccination dose in adolescent males aged 12 to 15 years (70.7 per million doses of the BNT162b2 vaccine), in adolescent males aged 16 to 17 years (105.9 per million doses of the BNT162b2 vaccine), and in young men aged 18 to 24 years (52.4 and 56.3 per million doses of the BNT162b2 vaccine and the mRNA-1273 vaccine, respectively).

Meaning  Based on passive surveillance reporting in the US, the risk of myocarditis after receiving mRNA-based COVID-19 vaccines was increased across multiple age and sex strata and was highest after the second vaccination dose in adolescent males and young men.

Abstract

Importance  Vaccination against COVID-19 provides clear public health benefits, but vaccination also carries potential risks. The risks and outcomes of myocarditis after COVID-19 vaccination are unclear.

Objective  To describe reports of myocarditis and the reporting rates after mRNA-based COVID-19 vaccination in the US.

Design, Setting, and Participants  Descriptive study of reports of myocarditis to the Vaccine Adverse Event Reporting System (VAERS) that occurred after mRNA-based COVID-19 vaccine administration between December 2020 and August 2021 in 192 405 448 individuals older than 12 years of age in the US; data were processed by VAERS as of September 30, 2021.

Exposures  Vaccination with BNT162b2 (Pfizer-BioNTech) or mRNA-1273 (Moderna).

Main Outcomes and Measures  Reports of myocarditis to VAERS were adjudicated and summarized for all age groups. Crude reporting rates were calculated across age and sex strata. Expected rates of myocarditis by age and sex were calculated using 2017-2019 claims data. For persons younger than 30 years of age, medical record reviews and clinician interviews were conducted to describe clinical presentation, diagnostic test results, treatment, and early outcomes.

Results  Among 192 405 448 persons receiving a total of 354 100 845 mRNA-based COVID-19 vaccines during the study period, there were 1991 reports of myocarditis to VAERS and 1626 of these reports met the case definition of myocarditis. Of those with myocarditis, the median age was 21 years (IQR, 16-31 years) and the median time to symptom onset was 2 days (IQR, 1-3 days). Males comprised 82% of the myocarditis cases for whom sex was reported. The crude reporting rates for cases of myocarditis within 7 days after COVID-19 vaccination exceeded the expected rates of myocarditis across multiple age and sex strata. The rates of myocarditis were highest after the second vaccination dose in adolescent males aged 12 to 15 years (70.7 per million doses of the BNT162b2 vaccine), in adolescent males aged 16 to 17 years (105.9 per million doses of the BNT162b2 vaccine), and in young men aged 18 to 24 years (52.4 and 56.3 per million doses of the BNT162b2 vaccine and the mRNA-1273 vaccine, respectively). There were 826 cases of myocarditis among those younger than 30 years of age who had detailed clinical information available; of these cases, 792 of 809 (98%) had elevated troponin levels, 569 of 794 (72%) had abnormal electrocardiogram results, and 223 of 312 (72%) had abnormal cardiac magnetic resonance imaging results. Approximately 96% of persons (784/813) were hospitalized and 87% (577/661) of these had resolution of presenting symptoms by hospital discharge. The most common treatment was nonsteroidal anti-inflammatory drugs (589/676; 87%).

Conclusions and Relevance  Based on passive surveillance reporting in the US, the risk of myocarditis after receiving mRNA-based COVID-19 vaccines was increased across multiple age and sex strata and was highest after the second vaccination dose in adolescent males and young men. This risk should be considered in the context of the benefits of COVID-19 vaccination.

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Article Information

Corresponding Author: Matthew E. Oster, MD, MPH, US Centers for Disease Control and Prevention, 1600 Clifton Rd, Atlanta, GA 30333 (eocevent416@cdc.gov).

Correction: This article was corrected March 21, 2022, to change “pericarditis” to “myocarditis” in the first row, first column of eTable 1 in the Supplement.

Accepted for Publication: December 16, 2021.

Author Contributions: Drs Oster and Su had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.

Concept and design: Oster, Shay, Su, Creech, Edwards, Dendy, Schlaudecker, Woo, Shimabukuro.

Acquisition, analysis, or interpretation of data: Oster, Shay, Su, Gee, Creech, Broder, Edwards, Soslow, Schlaudecker, Lang, Barnett, Ruberg, Smith, Campbell, Lopes, Sperling, Baumblatt, Thompson, Marquez, Strid, Woo, Pugsley, Reagan-Steiner, DeStefano, Shimabukuro.

Drafting of the manuscript: Oster, Shay, Su, Gee, Creech, Marquez, Strid, Woo, Shimabukuro.

Critical revision of the manuscript for important intellectual content: Oster, Shay, Su, Creech, Broder, Edwards, Soslow, Dendy, Schlaudecker, Lang, Barnett, Ruberg, Smith, Campbell, Lopes, Sperling, Baumblatt, Thompson, Pugsley, Reagan-Steiner, DeStefano, Shimabukuro.

Statistical analysis: Oster, Su, Marquez, Strid, Woo, Shimabukuro.

Obtained funding: Edwards, DeStefano.

Administrative, technical, or material support: Oster, Gee, Creech, Broder, Edwards, Soslow, Schlaudecker, Smith, Baumblatt, Thompson, Reagan-Steiner, DeStefano.

Supervision: Su, Edwards, Soslow, Dendy, Schlaudecker, Campbell, Sperling, DeStefano, Shimabukuro.

Conflict of Interest Disclosures: Dr Creech reported receiving grants from the National Institutes of Health for the Moderna and Janssen clinical trials and receiving personal fees from Astellas and Horizon. Dr Edwards reported receiving grants from the National Institutes of Health; receiving personal fees from BioNet, IBM, X-4 Pharma, Seqirus, Roche, Pfizer, Merck, Moderna, and Sanofi; and receiving compensation for being the associate editor of Clinical Infectious Diseases. Dr Soslow reported receiving personal fees from Esperare. Dr Schlaudecker reported receiving grants from Pfizer and receiving personal fees from Sanofi Pasteur. Drs Barnett, Ruberg, and Smith reported receiving grants from Pfizer. Dr Lopes reported receiving personal fees from Bayer, Boehringer Ingleheim, Bristol Myers Squibb, Daiichi Sankyo, GlaxoSmithKline, Medtronic, Merck, Pfizer, Portola, and Sanofi and receiving grants from Bristol Myers Squibb, GlaxoSmithKline, Medtronic, Pfizer, and Sanofi. No other disclosures were reported.

Funding/Support: This work was supported by contracts 200-2012-53709 (Boston Medical Center), 200-2012-53661 (Cincinnati Children’s Hospital Medical Center), 200-2012-53663 (Duke University), and 200-2012-50430 (Vanderbilt University Medical Center) with the US Centers for Disease Control and Prevention (CDC) Clinical Immunization Safety Assessment Project.

Role of the Funder/Sponsor: The CDC provided funding via the Clinical Immunization Safety Assessment Project to Drs Creech, Edwards, Soslow, Dendy, Schlaudecker, Lang, Barnett, Ruberg, Smith, Campbell, and Lopes. The authors affiliated with the CDC along with the other coauthors conducted the investigations; performed collection, management, analysis, and interpretation of the data; were involved in the preparation, review, and approval of the manuscript; and made the decision to submit the manuscript for publication.

Disclaimer: The findings and conclusions in this article are those of the authors and do not necessarily represent the official position of the CDC or the US Food and Drug Administration. Mention of a product or company name is for identification purposes only and does not constitute endorsement by the CDC or the US Food and Drug Administration.

Additional Contributions: We thank the following CDC staff who contributed to this article without compensation outside their normal salaries (in alphabetical order and contribution specified in parenthesis at end of each list of names): Nickolas Agathis, MD, MPH, Stephen R. Benoit, MD, MPH, Beau B. Bruce, MD, PhD, Abigail L. Carlson, MD, MPH, Meredith G. Dixon, MD, Jonathan Duffy, MD, MPH, Charles Duke, MD, MPH, Charles Edge, MSN, MS, Robyn Neblett Fanfair, MD, MPH, Nathan W. Furukawa, MD, MPH, Gavin Grant, MD, MPH, Grace Marx, MD, MPH, Maureen J. Miller, MD, MPH, Pedro Moro, MD, MPH, Meredith Oakley, DVM, MPH, Kia Padgett, MPH, BSN, RN, Janice Perez-Padilla, MPH, BSN, RN, Robert Perry, MD, MPH, Nimia Reyes, MD, MPH, Ernest E. Smith, MD, MPH&TM, David Sniadack, MD, MPH, Pamela Tucker, MD, Edward C. Weiss, MD, MPH, Erin Whitehouse, PhD, MPH, RN, Pascale M. Wortley, MD, MPH, and Rachael Zacks, MD (for clinical investigations and interviews); Amelia Jazwa, MSPH, Tara Johnson, MPH, MS, and Jamila Shields, MPH (for project coordination); Charles Licata, PhD, and Bicheng Zhang, MS (for data acquisition and organization); Charles E. Rose, PhD (for statistical consultation); and Scott D. Grosse, PhD (for calculation of expected rates of myocarditis). We also thank the clinical staff who cared for these patients and reported the adverse events to the Vaccine Adverse Event Reporting System.

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