Myocarditis and pericarditis

The outcomes of interest were diagnosis of myocarditis, pericarditis, and myopericarditis during a hospitalization or emergency department visit within 21 days following the second dose of an mRNA vaccine. Outcomes were assessed using International Classification of Diseases-10th Revision (ICD-10) codes. Myocarditis codes included I40.1 (isolated myocarditis), I40.8 (other acute myocarditis), I40.9 (acute myocarditis, unspecified), and I51.4 (myocarditis unspecified), and pericarditis codes included I30.0 (acute nonspecific idiopathic pericarditis), I30.8 (other forms of acute pericarditis), and I30.9 (acute pericarditis, unspecified).¹⁴ Myopericarditis was defined as any myocarditis or pericarditis ICD-10 code. For the cases identified through ICD-10 codes, a crosscheck was conducted using the Provincial Laboratory Information Solution data to determine if they were tested for at least 1 type of troponin within 30 days after their relevant vaccination dose. To be more specific with the outcome definition, a sensitivity analysis was conducted using a 7-days postvaccination risk period.