Lower Myocarditis Mortality Following mRNA COVID-19 Vaccination vs Viral Infection

Individuals who develop myocarditis after mRNA COVID-19 vaccination have a significantly lower mortality rate than individuals who develop viral infection-related myocarditis, according to study findings published in the Journal of the American College of Cardiology.

Investigators compared the prognosis between patients with myocarditis following the Pfizer-BioNTech BNT162b2 vaccine and patients with viral infection-related myocarditis for 180 days following diagnosis.

This retrospective cohort study used ICD-9 codes in the Hospital Authority of Hong Kong electronic public health care database linked with population-based vaccination records to identify 762 patients with viral infection-related myocarditis prepandemic (2000-2019), and 104 patients with post-BNT162b2 vaccination myocarditis (March 2021-March 2022). Patients were aged at least 12 years. The investigators used Cox proportional hazards models to examine the outcomes of heart failure, heart transplant, dilated cardiomyopathy, postdischarge health care utilization, and all-cause mortality.

Patients with a positive polymerase chain reaction test and those without elevated troponin levels during hospitalization were excluded. Patients with history of any of the examined diseases were also excluded. Patients were stratified by age (12-17 years, 18-59, and ≥60) and followed-up from diagnosis date (index date) for 180 days or the end of March 2022. Covariates in multivariable adjustment included sex, Charlson Comorbidity Index, receiving cardiovascular disease medications within the past year, health care utilization in the past year, and age.

Almost 9 million doses of BNT162b2 vaccine were administered to 3.98 million individuals in Hong Kong through March 2022. Among the 104 patients with post-vaccine myocarditis, 65.4% had received a second dose and 7.7% received a third dose. Other than the subgroup of older adults, there were more men than women in both cohorts.

Patients in the viral infection cohort had higher average Charlson Comorbidity Index scores, higher proportion of cardiovascular medication use, and higher health care utilization than patients in the postvaccination cohort.

In the 180-day follow-up period, investigators noted 84 deaths (11.0%) in the viral infection cohort and 1 death (1.0%) in the postvaccination cohort. They found 28 incidences (3.7%) of dilated cardiomyopathy in the viral infection cohort vs 1 case (1.0%) in the postvaccination cohort. There were 93 incidences (12.2%) of heart failure in the viral infection cohort vs 2 cases (1.9%) of heart failure in the postvaccination cohort.

The postvaccination cohort had a 92% lower mortality risk with adjust analysis (adjusted hazard ratio, 0.08; 95% CI, 0.01-0.57). There were no other significant differences in prognostic outcomes.

Study limitations include the retrospective design, as well as the potential for unconfirmed myocarditis diagnoses in the clinical data. There is also bias toward more severe myocarditis cases and failure to assess the impact of various treatments for myocarditis.

“This study found a significantly lower rate of mortality among individuals with myocarditis after mRNA vaccination compared with those with viral infection-related myocarditis,” the investigators wrote.  “The incidence of mortality, heart failure, heart transplant, and dilated cardiomyopathy within 180 days of myocarditis diagnosis among the former group is very rare.”

Disclosure: Some study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.