New Study Provides Reassuring Data on Myocarditis Heart Condition After mRNA COVID Vaccination

A new study published in The BMJ confirms previous reports of an increased risk of heart inflammation (myocarditis or myopericarditis) after vaccination with BNT162b2 (Pfizer-BioNTech) and mRNA-1273 (Moderna), but shows that the absolute number of cases was low, even in younger age groups, providing further evidence to support the overall safety of mRNA vaccines for Covid-19.

Only 1.6 cases per 100,000 in younger individuals (12-39 years) after Pfizer-BioNTech vaccine; Findings support the overall safety of mRNA vaccines for covid-19.

A study published today (December 16, 2021) by The BMJ provides more reassuring data on the risk of heart inflammation (myocarditis or myopericarditis) following mRNA vaccination against the covid-19 virus.

It confirms previous reports of an increased risk after vaccination with BNT162b2 (Pfizer-BioNTech) and mRNA-1273 (Moderna), but shows that the absolute number of cases was low even in younger age groups, providing further evidence to support the overall safety of mRNA vaccines for covid-19.

Myocarditis (inflammation of the heart muscle) and myopericarditis (inflammation of the outer layer of the heart) are rare but serious conditions, usually caused by a viral, bacterial, or fungal infection.

Recent reports and studies indicate an increased risk of heart inflammation after mRNA vaccination, especially after the second dose. But to date, no study has examined the association using information from an entire population.

To address this, researchers in Denmark used national health data to look for links between mRNA vaccination and a hospital diagnosis of myocarditis or pericarditis, elevated blood troponin levels (a measure of myocardial damage), and a hospital stay of more than 24 hours.

Their analyzes included nearly 5 million Danish residents aged 12 years or older who received either the Pfizer-BioNTech or Moderna vaccine.

The participants were followed from October 1, 2020 to October 5, 2021, taking into account a range of potentially influential factors, such as age, gender, vaccine priority group and underlying health conditions.

During follow-up, 269 participants developed myocarditis or myopericarditis, of whom 108 (40%) were aged 12-39 years and 196 (73%) were male.

Overall, the results show a strong association between Moderna vaccination and myocarditis or myopericarditis, while vaccination with Pfizer-BioNTech was only associated with an increased rate of myocarditis or myopericarditis in women.

The rate of myocarditis or myopericarditis was higher with Moderna vaccination than with Pfizer-BioNTech vaccination. Nevertheless, the absolute number of events after either vaccine was low and the cases were predominantly mild.

For example, of the 3,482,295 individuals vaccinated with Pfizer-BioNTech, 48 developed myocarditis or myopericarditis within 28 days of vaccination (an absolute rate of 1.4 per 100,000) compared to unvaccinated individuals.

In women the absolute percentage was 1.3 per 100,000 and in men 1.5 per 100,000. Among 12-39 year olds, the absolute rate was 1.6 per 100,000, and in the youngest age group (12-17 year olds) it was only 1 per 100,000 within 28 days of receiving the Pfizer-BioNTech vaccine.

Of the 498,814 subjects vaccinated with Moderna, 21 developed myocarditis or myopericarditis within 28 days of vaccination (an absolute rate of 4.2 per 100,000) compared to unvaccinated subjects.

In women the absolute percentage was 2 per 100,000 and in men 6.3 per 100,000. Among 12-39 year olds, the absolute rate was 5.7 per 100,000 within 28 days of receiving Moderna vaccine.

Both vaccines were also associated with approximately 50% less risk of cardiac arrest or death (the most serious manifestations of myocarditis or myopericarditis) compared to unvaccinated individuals.

In contrast, there was a 14-fold increased risk of cardiac arrest or death 28 days after a positive Covid-19 test compared to uninfected individuals.

This is an observational study, so cannot determine the cause, and the researchers point to some possible sources of bias, such as increased public awareness of potential side effects of vaccines, that may have influenced the results.

However, they say this was a well-designed study based on high-quality health data for an entire population, and the results were largely unchanged after additional analyses, suggesting they can stand close scrutiny.

As such, the researchers conclude that mRNA vaccination with Moderna and Pfizer-BioNTech is associated with an increased risk of myocarditis or myopericarditis in the Danish population, but the absolute rate following both vaccines was low, even in younger age groups.

The benefits of vaccination should be considered when interpreting these findings, they add, and larger multinational studies are needed to further investigate the risks of myocarditis or myopericarditis after vaccination within smaller groups.

Reference: “Study: SARS-CoV-2 Vaccination and Myocarditis or Myopericarditis: Population-Based Cohort Study” Dec 16, 2021, BMJ.
DOI: 10.1136 / bmj-2021-068665