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. 2022 Jun 1;5(6):e2218505.
doi: 10.1001/jamanetworkopen.2022.18505.

Epidemiology of Myocarditis and Pericarditis Following mRNA Vaccination by Vaccine Product, Schedule, and Interdose Interval Among Adolescents and Adults in Ontario, Canada

Sarah A Buchan  1   2   3 , Chi Yon Seo  1 , Caitlin Johnson  1 , Sarah Alley  1 , Jeffrey C Kwong  1   2   3   4   5 , Sharifa Nasreen  2   3 , Andrew Calzavara  3 , Diane Lu  1 , Tara M Harris  1 , Kelly Yu  1 , Sarah E Wilson  1   2   3
Affiliations

Epidemiology of Myocarditis and Pericarditis Following mRNA Vaccination by Vaccine Product, Schedule, and Interdose Interval Among Adolescents and Adults in Ontario, Canada

Sarah A Buchan et al. JAMA Netw Open. .

Abstract

Importance: Increased rates of myocarditis or pericarditis following receipt of COVID-19 mRNA vaccines have been observed. However, few available data are associated with differences in rates of myocarditis or pericarditis specific to vaccine products, which may have important implications for vaccination programs.

Objective: To estimate rates of reported myocarditis or pericarditis following receipt of a COVID-19 mRNA vaccine by product, age, sex, dose number, and interdose interval.

Design, setting, and participants: This population-based cohort study was conducted in Ontario, Canada (population: 14.7 million) from December 2020 to September 2021 and used data from Ontario's COVID-19 vaccine registry and passive vaccine-safety surveillance system. All individuals in Ontario, Canada, who received at least 1 dose of COVID-19 mRNA vaccine between December 14, 2020, and September 4, 2021, and had a reported episode of myocarditis or pericarditis following receipt of the COVID-19 vaccine during this period were included. We obtained information on all vaccine doses administered in the province to calculate reported rates of myocarditis or pericarditis.

Exposures: Receipt of a COVID-19 mRNA vaccine (mRNA-1273 [Moderna Spikevax] or BNT162b2 [Pfizer-BioNTech Comirnaty]).

Main outcomes and measures: All reports of myocarditis or pericarditis meeting levels 1 to 3 of the Brighton Collaboration case definitions were included. Rates and 95% CIs of reported cases of myocarditis or pericarditis per 1 000 000 mRNA vaccine doses administered were calculated by age, sex, dose number, vaccine product, and interdose interval.

Results: Among 19 740 741 doses of mRNA vaccines administered, there were 297 reports of myocarditis or pericarditis meeting the inclusion criteria; 228 (76.8%) occurred in male individuals, and the median age of individuals with a reported event was 24 years (range, 12-81 years). Of the reported cases, 207 (69.7%) occurred following the second dose of the COVID-19 mRNA vaccine. When restricted to individuals who received their second dose during the period of enhanced passive surveillance (on or after June 1, 2021), the highest rate of myocarditis or pericarditis was observed in male individuals aged 18 to 24 years following mRNA-1273 as the second dose (299.5 cases per 1 000 000 doses; 95% CI, 171.2-486.4 cases per 1 000 000 doses); the rate following BNT162b2 as the second dose was 59.2 cases per 1 000 000 doses (95% CI, 19.2-138.1 cases per 1 000 000 doses). Overall rates for both vaccine products were significantly higher when the interdose interval was 30 or fewer days (BNT162b2: 52.1 cases per 1 000 000 doses [95% CI, 31.8-80.5 cases per 1 000 000 doses]; mRNA-1273: 83.9 cases per 1 000 000 doses [95% CI, 47.0-138.4 cases per 1 000 000 doses]) compared with 56 or more days (BNT162b2: 9.6 cases per 1 000 000 doses [95% CI, 6.5-13.6 cases per 1 000 000 doses]; mRNA-1273: 16.2 cases per 1 000 000 doses [95% CI, 10.2-24.6 cases per 1 000 000 doses]).

Conclusions and relevance: The findings of this population-based cohort study of Ontario adolescents and adults with myocarditis or pericarditis following mRNA COVID-19 vaccination suggest that vaccine products and interdose intervals, in addition to age and sex, may be associated with the risk of myocarditis or pericarditis after receipt of these vaccines. Vaccination program strategies, such as age-based product considerations and longer interdose intervals, may reduce the risk of myocarditis or pericarditis following receipt of mRNA vaccines.

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Conflict of interest statement

Conflict of Interest Disclosures: Dr Buchan reported receiving grants from the Public Health Agency of Canada COVID-19 Immunity Task Force during the conduct of the study. Dr Kwong reported receiving grants from the Public Health Agency of Canada COVID-19 Immunity Task Force and being supported by a Clinician-Scientist Award from the University of Toronto Department of Family and Community Medicine during the conduct of the study. Dr Nasreen reported receiving grants from the Public Health Agency of Canada COVID-19 Immunity Task Force during the conduct of the study. Dr Wilson reported receiving grants from the Public Health Agency of Canada Canadian Immunity Task Force during the conduct of the study. No other disclosures were reported.

Figures

Figure.
Figure.. Overall Rate of Reported Myocarditis or Pericarditis Among People Who Completed the 2-Dose Vaccine Series With the Second Dose on or After June 1, 2021
Error bars indicate 95% CIs. BNT162b2, Pfizer-BioNTech Comirnaty; mRNA-1273, Moderna Spikevax.
See this image and copyright information in PMC

Comment in

References

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