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Assessing the temporal and cause-effect relationship between myocarditis and mRNA COVID-19 vaccines. A retrospective
Francesco Paolo Bianchi1, Donato Rizzi2, Antonio Daleno3
1Department of Interdisciplinary Medicine, Aldo Moro University of Bari, Bari, Italy; Azienda Ospedaliero Universitaria Policlinico Giovanni XXIII, Bari, Italy.
Objective:
In 2021, the US Centers for Disease Control and Prevention reported increased cases of myocarditis and pericarditis in the United States after mRNA COVID-19 vaccines. Our study aims to estimate the incidence of myocarditis in Apulia (Southern Italy) and the cause-effect relationship between COVID-19 mRNA vaccines and the risk of myocarditis.
Methods:
The Apulian regional archive of hospital discharge forms was used to define the cases of myocarditis in Apulia, considering data from 2017 to 2022. The overall vaccination status of patients was assessed via data collected from the Regional Immunization Database. The history of SARS-CoV-2 infection was extracted from the Italian Institute of Health platform.
Results:
Since 2017, 5687 cases of myocarditis have been recorded in Apulian subjects; the overall incidence described a decreasing trend, with a slight increase in 0-40 years-old subjects. From 2021 to 2022, 2,930,276 doses of COVID-19 mRNA vaccines were administered; a diagnosis of myocarditis after the second dose of the mRNA vaccine was reported for 894 (0.03%) of Apulian inhabitants, with an incidence rate of 17.9 × 1,000,000 persons-month. The multivariate analysis, adjusted for age, sex, underlying medical conditions, and diagnosis of COVID-19, showed that mRNA vaccination is a protective factor for myocarditis even in younger subjects (aOR = 0.4; 95% CI = 0.3-0.5).
Conclusion:
A temporal association between an exposure and an outcome is not equivalent to a causal association. Our study underlines how an approach that considers the other potential causes of myocarditis (primarily COVID-19) and a causality assessment must be prioritized in the study of the topic.
Insights
COVID-19 mRNA vaccines may protect against myocarditis, contrary to some reports. This study found vaccination to be a protective factor, even in younger individuals, highlighting the need to consider COVID-19 infection as a primary cause.
Area of Science:
- Epidemiology
- Vaccinology
- Cardiology
Background:
- Reports of increased myocarditis post-mRNA COVID-19 vaccination in the US.
- Need to assess myocarditis incidence and vaccine association in Southern Italy.
Purpose of the Study:
- Estimate myocarditis incidence in Apulia, Italy (2017-2022).
- Investigate the causal relationship between COVID-19 mRNA vaccines and myocarditis risk.
Main Methods:
- Utilized Apulian regional hospital discharge data (2017-2022) for myocarditis cases.
- Assessed vaccination status via Regional Immunization Database.
- Extracted SARS-CoV-2 infection history from the Italian Institute of Health.
Main Results:
- Recorded 5687 myocarditis cases in Apulia; overall incidence trended downward, with a slight rise in 0-40 year-olds.
- Post-vaccination myocarditis occurred in 0.03% of recipients (17.9 per 1,000,000 person-months).
- Multivariate analysis indicated mRNA vaccination is protective against myocarditis (aOR=0.4; 95% CI=0.3-0.5), even in younger demographics.
Conclusions:
- Temporal association does not imply causation.
- Prioritize causality assessment and consider other myocarditis causes, primarily COVID-19 infection.
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