The overall risk of heart inflammation (myopericarditis) following Covid-19 vaccination is very low, according to an international study published in The Lancet Respiratory Medicine.
The analysis of more than 11 studies found that myopericarditis affects 18 people per million vaccine doses, a lower incidence rate than all other viral vaccinations combined, for which the rate was 56 people per million doses.
The researchers analysed 20 studies covering more than 400 million vaccine doses
There have been reports of myopericarditis following mRNA-based Covid-19 vaccination, especially in adolescents and young adults. The study therefore set out to determine whether there was any substantive evidence to back up these claims.
To perform the analysis, the researchers examined international databases, looking at more than 400 million vaccination doses to compare the rate of heart inflammation following vaccination against Covid compared to other diseases.
In total, 11 studies looked at Covid-19 vaccinations, covering more than 395 million doses of the vaccine, of which nearly 300 million were mRNA vaccines.
The other nine studies looked at vaccinations such as such as smallpox (2.9 million doses), influenza (1.5 million doses), and others  (5.5 million doses).
Men and those below the age of 30 at higher risk of myopericarditis following vaccination
While the rate of myopericarditis following Covid-19 vaccination was 18 cases per million doses, certain factors did increase the risk of inflammation.
For example, the risk of myopericarditis was higher for those who received mRNA vaccines (22.6 cases per million doses) compared to non-mRNA vaccines (7.9 cases per million doses). Reported cases were also higher in people below the age of 30 (40.9 cases per million doses), males (23 cases per million doses), and following the second dose of Covid-19 vaccine (31.1 cases per million doses).
Co-author of the study, Dr Jyoti Somani, an infectious diseases specialist at National University Hospital, Singapore says that the results suggest that heart inflammation may be a potential side effect of any vaccination, not specifically Covid vaccinations.
He explains: The occurrence of myopericarditis following non-Covid-19 vaccination could suggest that myopericarditis is a side effect of the inflammatory processes induced by any vaccination and is not unique to the SARS-CoV-2 spike proteins in Covid-19 vaccines or infection.
“This also highlights that the risks of such infrequent adverse events should be offset by the benefits of vaccination, which include a lower risk of infection, hospitalisation, severe disease, and death from Covid-19.”
The benefits of Covid vaccines “far outweigh” the risks
The authors acknowledge some limitations to the study, including a lack of research of myopericarditis in children below the age of 12. The results can therefore not be generalised to this group.
In addition, comparisons have been made across different time periods for different vaccines. Diagnostic tools might have differed or not been available leading to lower reporting of cases in earlier studies.
In a linked commentary, Margaret Ryan of the Defence Health Agency and Clinical Professor at the University of California San Diego, USA, who was not involved in the study, said the results show that the benefits of vaccine “far outweigh risks in the midst of the current pandemic.”
“Nonetheless, scientific knowledge and public health strategies must continue to evolve. Alternative vaccine platforms, vaccine doses, or vaccine schedules may reduce the risk of rare adverse events following immunisation, and must be explored in the context of changing infection risk,” she concludes.