Study: Myocarditis Risk Is Significantly Higher After COVID-19 Infection Vs After Vaccine

The risk of myocarditis in unvaccinated individuals after a COVID-19 infection was at least 11 times higher than in individuals who developed myocarditis after receiving a COVID-19 vaccine or booster dose, according to the results of a study published in Circulation.

The detailed analysis included nearly 43 million individuals who were aged 13 years or older and received at least 1 dose of a COVID-19 vaccine in England between December 1, 2020, and December 15, 2021.

“We found that across this large dataset, the entire COVID-19-vaccinated population of England during an important 12-month period of the pandemic when the COVID-19 vaccines first became available, the risk of myocarditis following COVID-19 vaccination was quite small compared to the risk of myocarditis after COVID-19 infection,” Martina Patone, PhD, a statistician at the Nuffield Department of Primary Health Care Sciences at the University of Oxford in Oxford, England, said in a statement. “This analysis provides important information that may help guide public health vaccine campaigns, particularly since COVID-19 vaccination has expanded in many parts of the world to include children as young as 6 months old.”.

Investigators found that 2861 individuals were hospitalized or died, because of myocarditis during the 1-year period, and 617 of the case occurred during days 1 through 29 after receiving a COVID-19 vaccination.

Additionally, individuals who were infected with COVID-19 before receiving any doses of a vaccine were 11 times more at risk for developing myocarditis during days 1 through 28 of a positive COVID-19 infection, and the risk of COVID-19-related myocarditis was cut in half among individuals who were infected after vaccination.

The risk of myocarditis increased after the first dose of ChAdOx1 and after the first, second, and booster doses of any mRNA vaccines, but the risk was still lower compared with the risk of COVID-19-associated myocarditis, except for after a second dose of the Moderna vaccine.

However, investigators found that the myocarditis risk was found to be higher during days 1 through 28 after a second dose of the Moderna vaccine for all ages and genders.

Individuals who received the booster dose of the Moderna vaccine were, on average, younger than those who received booster doses of ChAdOx1 or the Pfizer-BioNTech vaccine.
Women under aged 40 years had a slightly increased risk of myocarditis after receiving a second dose of the Moderna vaccine while women who were older than aged 40 years had an increased risk after a first or third dose of the Pfizer-BioNTech vaccine.

For both groups, the risk of infection-associated myocarditis was higher compared with the vaccine-associated risk.

Men who were aged 40 years or younger had an increased risk after the first dose of either the mRNA vaccine or a second dose of any of the 3 available COVID-19 vaccines in England during the study period. The risk also increased in men who were younger than aged 40 years after receiving 2 Moderna doses compared with the risk of myocarditis after a COVID-19 infection.

In men who aged 40 years or older, there was a slight increased risk of myocarditis after a booster dose of either mRNA vaccine.

For both groups, the risk of infection-associated myocarditis was higher compared with the vaccine-associated risk.

Investigators evaluated England’s National Immunization database of COVID-19 vaccinations for all individuals aged 13 years or older who received at least a 2-dose adenovirus-vector developed by the University of Oxford and AstraZeneca, a 1 dose of the ChAdOx1 vaccine, the Moderna vaccine, or the Pfizer-BioNTech vaccine.

The database included information about the dates administered, demographic information, the dosing sequence, and type of vaccine. About 6 million individuals tested positive for a COVID-19 infection either before or after a COVID-19 vaccination during the study period.

Investigators also matched these data with data on COVID-19 infection, hospital admission, and death certificates for the same time period. All individuals were classified based on age and sex to determine which groups had the highest risk of myocarditis.

Additionally, investigators used the self-controlled case series method to estimate the relative incidence of an acute event in a predefined post-vaccination risk period, which was from 1 to 28 days, and compared it with other times, including pre-vaccination and long after the vaccination.

Reference

Myocarditis risk significantly higher after COVID-19 infection vs. after a COVID-19 vaccine. News release. EurekAlert. August 22, 2022. Accessed August 23, 2022. https://www.eurekalert.org/news-releases/962244