Another study shows COVID-19 vaccine-associated myocarditis rare
An analysis of nationwide data across four Nordic countries shows risk for myocarditis is rare but is highest among young males after a second COVID-19 vaccine dose.
“This risk should be balanced against the benefits of protecting against severe COVID-19 disease,” the researchers wrote.
The findings suggest risk for myocarditis and pericarditis, while small, was highest after a second dose of a messenger RNA (mRNA) COVID-19 vaccine for males aged 16 to 24 years, compatible with four to seven excess events in 28 days per 100,000 vaccinees after the BNT162b2 (Pfizer-BioNTech) vaccine and nine to 28 excess events per 100,000 vaccinees after mRNA-1273 (Moderna) vaccine.
“These extra cases among men aged 16 to 24 years correspond with a fivefold increased risk after the Pfizer vaccine and 15-fold increased risk after the Moderna vaccine compared with those who are unvaccinated,” Rickard Ljung, MD, PhD, MPH, professor and physician with the division of use and information at Swedish Medical Products Agency in Uppsala, Sweden, told Healio.
Greater risk after second dose
Ljung and colleagues conducted population-based cohort studies in Denmark, Finland, Norway and Sweden, using linked data from nationwide health registers on SARS-CoV-2 vaccination, myocarditis and pericarditis diagnoses for 23,122,522 people aged at least 12 years. Researchers followed the cohorts from December 2020 until incident myocarditis or pericarditis, censoring, or October 2021, analyzing each cohort separately and then combining results by meta-analysis. Exposures included the 28-day risk periods after administration date of the first and second doses of a SARS-CoV-2 vaccine, including the Moderna vaccine, Pfizer-BioNTech vaccine, AZD1222 (AstraZeneca) vaccine or any combination thereof. A homologous schedule was defined as receiving the same vaccine type for both doses.
Researchers assessed the outcomes for date of first inpatient hospital admission based on primary or secondary discharge diagnosis for myocarditis or pericarditis and incident myocarditis or pericarditis combined from either inpatient or outpatient hospital care.
The findings were published in JAMA Cardiology.
Across the cohorts, 81% of people were vaccinated by the end of the study (50.2% female).
Researchers observed 1,077 incident myocarditis events and 1,149 incident pericarditis events. For males and females who received a homologous schedule, the second mRNA vaccine dose was associated with higher risk for myocarditis within the 28-day period, with adjusted incidence rate ratios (IRRs) of 1.75 (95% CI, 1.43-2.14) for the Pfizer-BioNTech vaccine and 6.57 (95% CI, 4.64-9.28) for the Moderna vaccine.
In analyses restricted to adolescent boys and young men aged 16 to 24 years, adjusted IRRs were significantly higher, at 5.31 (95% CI, 3.68-7.68), after a second dose of Pfizer-BioNTech vaccine and 13.83 (95% CI, 8.08-23.68) after a second dose of the Moderna. Numbers of excess events were 5.55 (95% CI, 3.7-7.39) events per 100,000 vaccinees after the second dose of the Pfizer-BioNTech vaccine and 18.39 (95% CI, 9.05-27.72) events per 100,000 vaccinees after the second dose of the Moderna vaccine. Estimates for pericarditis were similar, according to the researchers.
“The risks of myocarditis and pericarditis were highest within the first 7 days of being vaccinated, were increased for all combinations of mRNA vaccines, and were more pronounced after the second dose,” the researchers wrote. “A second dose of mRNA-1273 had the highest risk of myocarditis and pericarditis, with young males aged 16 to 24 years having the highest risk.”
Ljung told Healio the researchers are now analyzing the risk for myocarditis after a third vaccine dose.
“We are also analyzing the prognosis after myocarditis,” Ljung said.
Myocarditis risk ‘real but low’
In a related editorial, Ann Marie Navar, MD, PhD, of the division of cardiology at the University of Texas Southwestern Medical Center in Dallas, and Robert O. Bonow, MD, of the division of cardiology at Northwestern University Feinberg School of Medicine, wrote that risk for myocarditis after COVID-19 immunization “is real, but this low risk must be considered in context of the overall benefit of vaccine.”
The data also demonstrate the risk of vaccine-associated myocarditis is “not homogeneous,” disproportionately affecting young men and adolescent boys and occurring more frequently after Moderna vaccine vs. the Pfizer-BioNTech vaccine.
“At the individual level, immunization prevents not only COVID-19-related myocarditis but also severe disease, hospitalization, long-term complications after COVID-19 infection and death,” Navar and Bonow wrote. “At the population level, immunization helps to decrease community spread, decrease the chances of new variants emerging, protect people who are immunocompromised, and ensure our health care system can continue to provide for our communities.”
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For more information:
Rickard Ljung, MD, PhD, MPH, can be reached at rickard.ljung@lakemedelsverket.se.
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