(367) VAC4EU study to identify risk factors and characterize the clinical course of myocarditis/pericarditis following mRNA-1273 vaccination in four European countries: first descriptive analyses

Background: Myocarditis and pericarditis are recognized as possible adverse events of special interest (AESIs) following mRNA-1273 vaccination. Prior research indicates these events predominantly occur in young males and after the second dose of the vaccine. However, comprehensive studies on other potential risk factors are lacking.

Objectives: These interim analyses sought to identify possible risk factors for myocarditis and pericarditis among individuals vaccinated with mRNA-1273.

Methods: This case-cohort study utilized secondary health data from five VAC4EU network data access partners across four European countries (national registries in Denmark and Norway, VID and SIDIAP in Spain and CPRD Aurum in the UK). Inclusion criteria for the base cohort were receival of at least one dose of mRNA-1273 between 6 January 2021 and 31 August 2024, a minimum one year enrolment in the participating databases before vaccination, and no diagnosis of myocarditis/pericarditis in the six months preceding vaccination. Cases were identified within 30 days following vaccination using diagnostic codes, and a 1:4 calendar-time matched control sample was selected from the base cohort. Preliminary analysis included demographic assessments, medical history (comorbidities, medication use, healthcare utilization), and vaccination history for both cases and controls. Federated analyses were performed using the ConcePTION common data model.

Results: The analysis included the following number of mRNA-1273 recipients (and respective myocarditis and pericarditis cases): 679,702 in Danish national registries (45 and 52 cases); 2,120,376 in VID (20 and 70 cases); 266,558 in SIDIAP ( < 5 cases each); and 1,544,983 in Norwegian registries (80 and 138 cases). Data from CPRD Aurum (UK) were pending at the time of this report. The proportion of male cases was 70-89% for myocarditis and 65-79% for pericarditis, compared to a more balanced sex distribution in controls (up to 54% males). Myocarditis cases were younger than controls, with no apparent differences in medical history. Pericarditis cases had more pronounced healthcare utilization and comorbidities compared to controls.

Conclusions: Preliminary findings suggest age and sex to be potential risk factors for the occurrence of myocarditis/pericarditis after mRNA-1273 vaccination. In addition, comorbidities and prior healthcare utilization may be potential risk factors for the occurrence of pericarditis.