The overall risk of developing myopericarditis following vaccination for Covid-19 is very low, at just 18 cases per million doses, new research involving over 400 million people worldwide has found.

According to the findings, the risk of developing myopericarditis following vaccination against Covid-19 is comparable to, or lower than, the risk following non-Covid vaccinations, which currently stands at 56 cases per million doses.

Myopericarditis is a condition that causes inflammation of the heart muscle. In some cases, it can cause severe and permanent heart damage. It is most often caused by viruses, but in rare instances, it can also occur after vaccination.

During the pandemic, there were reports of myopericarditis following vaccination with mRNA vaccines, especially in adolescents and young adults. This study aimed to determine whether this increase in reporting was due to a true increase in incidence or as a result of improved reporting systems and recall bias.

Researchers analysed over 20 studies from international databases with reported incidences of myopericarditis following any type of vaccination between January 1947 and December 2021. Of these, 11 studies looked specifically at Covid vaccinations, covering over 395 million Covid vaccine doses, nearly 300 million of which were mRNA vaccines.

The rest of the studies covered other vaccinations such as smallpox, influenza, polio, diphtheria, typhoid, hepatitis, measles, mumps and rubella.

The researachers found no statistically significant difference between the incidence of myopericarditis following Covid-19 vaccination and other vaccinations.

“Our research suggests that the overall risk of myopericarditis appears to be no different for this newly approved group of vaccines against Covid-19 compared to vaccines against other diseases. The risk of such rare events should be balanced against the risk of myopericarditis from infection and these findings should bolster public confidence in the safety of Covid vaccinations,” commented study author, Dr Kollengode Ramanathan, of National University Hospital in Singapore.

The research found that the rate of myopericarditis following Covid-19 vaccination was 18 cases per million doses, although the risk 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).

In order to put the findings into context, the researchers conducted a post-study analysis. They found that among 2.5 million patients who were hospitalised with Covid-19, many of whom had clinical or radiological suspicion for myopericarditis, 1.1% actually had the condition.

However, while these figures provide a frame of reference, the researchers noted that the results are not directly comparable with the number of cases of myopericarditis following Covid-19 vaccination due to different units of measurement.

“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,” commented study co-author, Dr Jyoti Somani, of National University Hospital in Singapore.

This study is published in the journal, The Lancet Respiratory Medicine.