A Study to Learn About The COVID-19 (Study) Vaccine (Called COMIRNATY) in People That Are Less Than 21 Years Old.

Inclusion Criteria:

• Cohort 1/2:

1. Age <21 years.

2. Presentation to participating medical center with evaluation in Emergency Roomand/or hospitalization.

3. Received either the 1st, 2nd, 3rd or booster dose(s) of COMIRNATY within 28days of symptom onset.

4. Meets criteria of Centers for Disease Control and Prevention case definition ofprobable or confirmed myocarditis/pericarditis

5. Capable of giving signed informed consent/assent (by parents/legal guardians ofminors and/or patients), which includes compliance with the requirements andrestrictions listed in the Informed Consent/Assent Document and in thisprotocol OR meets criteria for waiver of consent.

• Cohort 3:

1. Age <21 years.

2. Presentation to participating medical center with evaluation in Emergency Roomand/or hospitalization.

3. COVID-19-related disease

4. Acute COVID-19 infection OR

5. Multi-system Inflammatory Syndrome in Children Associated with COVID-19 (MIS-C) AND

6. Probable or confirmed myocarditis/pericarditis* not temporally related tovaccination with COMINARTY

7. Probable myocarditis/pericarditis as defined by ≥ 1 new finding of:

• Elevated troponin above upper limit of normal
• Abnormal ECG or rhythm monitoring finding consistent with myocarditis
• Abnormal cardiac function or wall motion abnormalities onechocardiogram
• cMRI findings consistent with myocarditis OR

2. Confirmed myocarditis/pericarditis as defined by:

• Histopathologic confirmation of myocarditis OR
• Elevated troponin above upper limit of normal AND cMRI findingsconsistent with myocarditis

5. Capable of giving signed informed consent/assent (by parents/legal guardians ofminors and/or patients), which includes compliance with the requirements andrestrictions listed in the Informed Consent/Assent Document and in thisprotocol OR meets criteria for waiver of consent.

Exclusion Criteria:

1. A plausible alternative etiology for myocarditis/pericarditis, as determined by thesite based upon their routine clinical practice for evaluation of potential causesfor myocarditis/pericarditis.

2. Pre-existing cardiac conditions that could impact the primary endpoint, includingbut not limited to, documented history of left ventricular dysfunction (e.g.,cardiomyopathy or myocardial infarction), pacemaker, or congenital heart disease,with the exceptions of:

3. Bicommissural aortic valve with < trivial stenosis and/or insufficiency

4. Mitral valve prolapse with < trivial insufficiency

5. Hemodynamically insignificant atrial septal or ventricular septal defects.

6. Previous administration with an investigational drug or vaccine within 30 days ofenrollment (or as determined by the local requirement).