This is a national multicenter study in Norway investigating of individuals with Covid-19 vaccine associated myocarditis (VAM) and pericarditis in Norway.

The main objective is to validate the reported possible cases of Covid-19 vaccine associated myo-and pericarditis in Norway as well as investigate for predisposing factors and risk factors for developing these vaccine adverse events.

Furthermore, patients with confirmed Covid-19 VAM, will be invited to participate in a prospective cohort study, investigating for cardiac long-term adverse effects 1 year and 2 years after vaccine-associated myocarditis.

Myocarditis and pericarditis following vaccination with Covid-19 vaccines has been reported as rare but unexpected and potentially severe vaccine adverse events.

In Norway, all vaccines administrated are registered in the national vaccine registry (SYSVAK). All in-hospital diagnoses are reported in a national diagnosis registry (NPR). These complete national high-quality registers allow linking diagnosis of myocarditis and pericarditis to vaccine data (date, product, dose number) on an individual level.

Oslo University Hospital, in collaboration with the Norwegian Institute of Public Health and the Norwegian Medicines Agency, will perform a study consisting of 2 parts:

Part 1 "Validation study":

Eligible patients for inclusion are all individuals with suspected / reported Covid - 19 vaccine associated pericarditis and myocarditis in Norway from 2021 and onwards. Patients will be identified by linking data from the Norwegian Patient registry NPR (ICD-10 diagnostic codes for pericarditis and myocarditis) and the Immunization registry (SYSVAK) (< 90 days since vaccination). The diagnosis of Covid-19 vaccine associated pericarditis and myocarditis will then be confirmed or rejected by medical record search according to international accepted Brighton criteria. The Brighton collaboration criteria provide evidence levels of diagnostic certainty of myocarditis and pericarditis based on cardiac signs and symptoms, cardiac enzymes, ECG findings, imaging studies and histopathology.The criteria is used to distinguish between suspected, probable and confirmed diagnosis of myocarditis and pericarditis. Patients with another more likely reason for confirmed myocarditis or pericarditis by Brighton will not be classified with Covid-19 vaccine associated myocarditis (VAM) or pericarditis, respectively.

Part 2 "Clinical follow-up study" All patients identified in the validation study with confirmed Covid-19 VAM will be invited to participate in the prospective clinical follow-up study (all age groups, both sexes, all geographical areas of Norway). Inclusion wil be by informed consent. Data collection, symptom reporting and cardiac examinations (clinical examination, ECG, 24 hours Holter ECG, echocardiography, cardiac magnetic resonance imaging) will be performed at 1 and 2 years after a diagnosis of Covid -19 VAM. Blood analyses will be performed and a blood sample stored in a biobank in consenting participants. Clinical endpoints will be collected at 1 and 2 years follow-up.

Part 1 Individuals identified with possible Covid-19 vaccine associated myocarditis and pericarditis, by linkage of diagnosis of myocarditis and pericarditis (from Norwegian Patient Registry, NPR) and vaccination data (Immunization registry, SYSVAK).

Part 2.

Inclusion Criteria:

• Confirmed myocarditis (definite, probable, possible) by Brighton criteria < 90 days after either Covid-19 vaccine.

Exclusion Criteria:

• Other more likely cause of myocarditis, including Covid-19 infection.

Patients with Covid-19 vaccine associated myocarditis and pericarditis