Myocarditis risk significantly higher after COVID-19 infection vs. after a COVID-19 vaccine
In a detailed analysis of nearly 43 million people, the risk of myocarditis in unvaccinated individuals after COVID-19 infection was at least 11 times higher compared to people who developed myocarditis after receiving a COVID-19 vaccine or booster dose, according to new research published in the American Heart Association’s flagship, peer-reviewed journal Circulation.
This analysis included data from England’s National Immunization database for people ages 13 and older who received at least one dose of a COVID-19 vaccine between December 1, 2020 and December 15, 2021 in England.
Several previous studies and reports from public health agencies around the world including the U.S. Centers for Disease Control and Prevention have highlighted a possible connection and potentially increased risk of myocarditis after receiving an mRNA COVID-19 vaccine, generating considerable scientific, policy and public interest.
In this study, researchers evaluated England’s National Immunization database of COVID-19 vaccinations for all people ages 13 or older who had received at least one dose of the ChAdOx1 (a two-dose adenovirus-vector COVID-19 vaccine developed by the University of Oxford and AstraZeneca, most similar to the one-dose Johnson & Johnson/Janssen COVID-19 vaccine available in the U.S.), the Pfizer-BioNTech or the Moderna COVID-19 vaccine (the same mRNA vaccines available in the U.S.) between December 1, 2020 and December 15, 2021. This dataset totaled nearly 43 million people, which included more than 21 million who had received a booster dose of any of the COVID-19 vaccines (meaning they had received a total of 3 doses of a COVID-19 vaccine). The database detailed the type of COVID-19 vaccines received, dates received and dose sequencing, along with individual demographic information including age and sex for each individual. Nearly 6 million people tested positive for COVID-19 infection either before or after COVID-19 vaccination during the study period.
England’s National Immunization database records were then cross-referenced and matched to the national offices with data on COVID-19 infection, hospital admission and death certificates for the same time period, December 1, 2020 through December 15, 2021. Individuals were classified based on age and sex to reveal which groups had the highest risk of myocarditis after a COVID-19 vaccine or after COVID-19 infection and hospitalization. The authors used the self-controlled case series (SCCS) method, which was developed to estimate the relative incidence of an acute event in a pre-defined post-vaccination risk period (1-28 days), compared to other times (pre-vaccination or long after vaccination). Being a within-person comparison, the analyses were controlled to adjust for any fixed characteristics, including sex, race or ethnicity, or chronic health conditions.
In the overall dataset of nearly 43 million people, the analyses found:
- Fewer than 3,000 (n=2,861), or 0.007%, people were hospitalized or died with myocarditis during the one-year study period. 617 of these cases of myocarditis occurred during days 1-28 after receiving a COVID-19 vaccination, of which 514 were hospitalized.
- People who were infected with COVID-19 before receiving any doses of the COVID-19 vaccines were 11 times more at risk for developing myocarditis during days 1-28 after a COVID-19 positive test.
- The risk of COVID-19 infection-related myocarditis risk was cut in half among people infected after vaccination (received at least one dose of a COVID-19 vaccine).
- The risk of myocarditis increased after a first dose of the ChAdOx1 COVID-19 vaccine (an adenovirus-vector vaccine most similar to the Johnson & Johnson/Janssen COVID-19 vaccine available in the U.S.) and after a first, second and booster dose of any of the mRNA COVID-19 vaccines. However, the risk of vaccine-associated myocarditis was lower compared to the risk of COVID-19 infection-associated myocarditis, except for after a second dose of the Moderna vaccine.
- Myocarditis risk was found to be higher during days 1-28 after a second dose of the Moderna COVID-19 vaccine for people of all genders and ages, and the risk also persisted after a booster dose of the Moderna vaccine. However, people receiving a booster dose of Moderna were, on average, younger in comparison to those who received a booster dose of the ChAdOx1 or Pfizer-BioNTech vaccine, therefore, results may not be generalizable to all adults.
