Myocarditis risk ‘significantly higher’ with COVID-19 vs. vaccination
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Data from a large cohort in England suggest that risk for myocarditis, while small overall, is significantly higher after SARS-CoV-2 infection in unvaccinated individuals vs. after COVID-19 vaccination, researchers reported.
In an analysis of more than 42 million vaccinated children and adults, researchers also found that although the risk for myocarditis with SARS-CoV-2 infection remained after vaccination, it was “substantially reduced,” suggesting vaccination provides some protection from the CV consequences of SARS-CoV-2. Additionally, risk for myocarditis after vaccination, while still small, was higher among men aged 40 years or younger, particularly after a second dose of the Moderna COVID-19 vaccine.
“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 press release. “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.”
Overall myocarditis risk small
In a self-controlled case series, Patone and colleagues analyzed data from 42,842,345 children and adults aged at least 13 years who received at least one dose of the COVID-19 vaccine in England between December 2020 and December 2021.
Researchers evaluated the association between vaccination and myocarditis, stratified by age and sex, estimating the incidence rate ratio and excess number of hospital admissions or deaths from myocarditis per 1 million people for the 1 to 28 days after sequential vaccine doses or a positive COVID-19 test.
The findings were published in Circulation.
Within the cohort, 21,242,629 people received three vaccine doses and 13.9% had a confirmed SARS-CoV-2 infection, including 49.8% before their first vaccine dose.
Myocarditis occurred in 0.007% of people, with 617 events occurring 1 to 28 days after vaccination; 0.001% of patients died within 28 days after hospital admission for myocarditis. Researchers found risk for myocarditis was increased in the 1 to 28 days after a first dose of the AstraZeneca vaccine, with an incidence rate ratio of 1.33 (95% CI, 1.09-1.62) and a first, second and booster dose of the Pfizer/BioNtech vaccine, with IRRs of 1.52 (95% CI, 1.24-1.85]; 1.57 (95% CI, 1.28-1.92); and 1.72 (95% CI, 1.33-2.22), respectively. However, risks were lower than the risks after a positive SARS-CoV-2 test before vaccination (IRR = 11.14; 95% CI, 8.64-14.36) and after vaccination (IRR = 5.97; 95% CI, 4.54-7.87).
Small but greater risk for younger men
Among vaccinated men, 34.4% were younger than age 40 years. Risk for myocarditis was higher 1 to 28 days after a second dose of the Moderna vaccine, with an IRR of 11.76 (95% CI, 7.25-19.08) and persisted after a booster dose (IRR = 2.64; 95% CI, 1.25-5.58).
The associations were stronger among men younger than age 40 years for all vaccines. Among men younger than age 40 years, the number of excess myocarditis events per 1 million people was higher after a second dose of the Moderna vaccine than after a positive SARS-CoV-2 test, (97 excess events per 1 million vs. 16 excess events per 1 million).
Among women younger than age 40 years, the number of excess events per million was similar after a second dose of the Moderna vaccine and a positive test (7 excess events per 1 million vs. 8 excess events per 1 million).
“These findings may justify some reconsideration of the selection of vaccine type, the timing of vaccine doses, and the net benefit of booster doses in young people, particularly in young men,” the researchers wrote.
The researchers noted that the average age of those receiving the Moderna vaccine was younger — age 32 years — compared with other vaccines where recipients were in their mid-40s and 50s, adding that the observed excess risk related to the Moderna vaccine may be a result of the higher probability of myocarditis in this younger age group.
“The risk of hospital admission or death from myocarditis is greater after SARS- CoV-2 infection than COVID-19 vaccination and remains modest after sequential doses including a booster dose of BNT162b2 mRNA vaccine,” the researchers wrote. “However, the risk of myocarditis after vaccination is higher in younger men, particularly after a second dose of the [Moderna] vaccine.”
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