A study in JAMA Network in August 2024 explores the link between myocarditis and COVID-19 infection or vaccination. The nationwide cohort study considered 4,635 patients hospitalised for myocarditis in France during the first 1.5 years after the introduction of COVID-19 vaccination. The authors found that patients with post-COVID-19 mRNA vaccination myocarditis showed a “lower frequency” of cardiovascular complications than those with “conventional myocarditis” at 18 months. However, they emphasise the need for medical management “up to several months” after discharge for affected patients.
Risk of myocarditis
After “broadly” reported cases of myocarditis after vaccination with the COVID-19 mRNA BNT162b2 and mRNA-1273 vaccines, studies confirmed an increased risk of myocarditis after vaccination. This is predominantly in young adults and after the second dose. However, the authors note that SARS-CoV-2 infection in the previous month is also associated with a risk of myocarditis.
“Although vaccination resulted in a significant decrease in hospitalisation and mortality from COVID-19, it is crucial to evaluate the consequences of postvaccine myocarditis, particularly in young people, who are less likely to have serious illness after SARS-CoV-2 infection and could thus be less inclined toward vaccination.”
The study
The study was intended to examine the cardiovascular complications of postvaccine myocarditis and other types of myocarditis during an 18-month follow-up, as well as disease management and discharge. The authors used data from the French national hospital discharge database (PMSI), the French national COVID-19 vaccination database (VAC-SI), the SARS-CoV-2 diagnosis testing database (SI-DEP), and the National Health Data System (SNDS), covering the 67 million residents of France.
The cohort comprised individuals between 12 and 49 years who had a “main or related diagnosis of myocarditis” from inpatient hospital care from 27th December 2020 to 30th June 2022:
- Postvaccine myocarditis – individuals admitted to hospital for myocarditis within 7 days after receipt of any dose of a COVID-19 mRNA vaccine: 558 (12%).
- Post-COVID-19 myocarditis – individuals admitted to hospital for myocarditis within 30 days of SARS-CoV-2 infection and who did not receive an mRNA vaccination within the preceding 7 days: 298 (6%).
- Conventional myocarditis – remaining cases of myocarditis: 3779 (82%).
- Excluded – 7 individuals had a history of both COVID-19 mRNA vaccination within 7 days and COVID-19 within 30 days.
Findings
The study is the first to describe the “evolution” of postvaccine myocarditis with an 18-month follow-up after hospitalisation. It found that patients with postvaccine myocarditis had fewer hospital readmissions for myopericarditis, other cardiovascular events, or all-cause death as a composite outcome than those with conventional myocarditis. This contrasts with patients with post-COVID-19 myocarditis.
The researchers suggest that the lower incidence of all-cause hospitalisation observed in postvaccine myocarditis compared with conventional myocarditis “might be explained” by the “more varied aetiology” of conventional myocarditis cases. They offer the example of cases linked to inflammatory disease, which may require more follow-up due to underlying pathology.
While the authors recognise that post-COVID-19 mRNA vaccination myocarditis have a lower frequency of cardiovascular complications than those with conventional myocarditis, “contrary to patients with post-COVID-19 myocarditis”, they highlight the importance of medical disease management for “up to several months after hospital discharge”.
“These elements should all be taken into account for ongoing and future mRNA vaccine recommendations”.
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