ACUTE PERICARDITIS; This 65-year-old, male subject was participating in A Study.  The subject's medical history, as provided by the investigator, included hypertension, diabetes mellitus type II, attention deficient hyperactivity disorder, contact dermatitis (sea life, snorkeling), bursitis of olecranon of right elbow, benign prostatic hypertrophy with outflow obstruction, hiatal hernia, hypercholesterolemia, and gastroesophageal reflux disease. Concomitant medications reported included atorvastatin, prasugrel, acetylsalicylic acid, lisinopril, metoprolol succinate, simvastatin, and metformin.  While participating in this study, and preceding this event, the subject experienced the serious adverse event of myocardial infarction (MOD-2020-000566).  Prior to event onset, the subject received intramuscular mRNA-1273 (Dose 2) SARS-CoV-2 vaccination on 01 Sep 2020, approximately 2 months and 12 days days before onset of the event.  On 24 Oct 2020, the subject was hospitalized for non-ST-elevation myocardial infarction.   On 26 Oct 2020, he underwent percutaneous coronary intervention of ramus intermedius with placement of drug eluting stents and was discharged on acetylsalicylic acid, prasugrel, and statin therapy beta-blocker. Post discharge, he had been doing well.  On 12 Nov 2020, the subject experienced acute pericarditis and was hospitalized. He presented to the emergency room with the complaint of chest pain for two nights, which was worse in supine position and better when sitting upright. Physical examination showed normal heart rhythm with S1 and S2. Chest x-ray showed no acute infiltrates. Electrocardiogram showed incomplete right bundle branch block and left anterior fascicular block. Echocardiogram revealed: preserved biventricular size and systolic function with left ventricular ejection fraction of 55-60%; no regional wall abnormality; mild aortic valve sclerosis with normal function; no significant valvular abnormality with normal right ventricular systolic pressure; no pericardial effusion. Troponin, c-reactive protein, and erythrocyte sedimentation rate were normal. Additional laboratory results included: international normalized ratio 1.0, albumin 4.3, alkaline phosphatase 81, aspartate aminotransferase 26, alanine aminotransferase 35, total bilirubin 0.42, thyroid stimulating hormone 1.86, sodium 134, potassium 4.4, chloride 100, carbon dioxide 22, blood urea nitrogen 22, creatinine 0.74, calcium 9.4, white blood cell count 7.8, hemoglobin 15.3, hematocrit 43.7 and platelet count 266. The subject was evaluated by a cardiologist who assessed the event as acute pericarditis with possible dressler syndrome. Treatment included colchicine 0.6 mg twice daily, and proton pump inhibitor.   On 13 Nov 2020, vital signs included temperature 98 degrees Fahrenheit, pulse 57 beats per minute, respiratory rate 18 breaths per minute, blood pressure 117/75 mmHg and oxygen saturation 96%. Laboratory results included cholesterol 80, low-density lipoprotein 23, high-density lipoprotein 31, triglycerides 180, sodium 136, potassium 4.4, chloride 103, carbon dioxide 23, blood urea nitrogen 23, creatinine 0.74, calcium 9.3, white blood cell count 5.9, hemoglobin 14.7, hematocrit 41.8 and platelet count 225. On the same day, the subject reported feeling better and was discharged from the hospital on oral (PO) colchicine for 3 months, PO ibuprofen three times a day for one week, and PO pantoprazole. The subject was instructed to follow-up in clinic for repeat basic metabolic panel and complete blood count, and follow-up with cardiology.   The subject received all scheduled doses of study drug prior to the event; therefore, action taken with study drug in response to the event was not applicable.  The event, acute pericarditis, was reported as resolved on 13 Nov 2020.  The investigator assessed the event, acute pericarditis, as not related to study drug and not related to study procedure.  Follow-up received on 15 Dec 2020 included updated medical history, severity (previously grade 2), event end date, and outcome.  Follow-up received on 26 Apr 2022 included updated concomitant medications and event severity grade (previously grade 4).  Company comment: This case concerns a 65-year-old, male subject with medical history of hypertension, diabetes mellitus type II and hypercholesterolemia, among others, and recent event of myocardial infarction, who experienced the unexpected event of acute pericarditis. The event occurred 3 months 9 days after the first dose of blinded study vaccine administration and 2 months 12 days after the last dose administration. The event, acute pericarditis, was reported as resolved. The event was considered unrelated to the study vaccine in agreement with the Investigator's assessment, noting the proximate event of myocardial infarction as a potential risk factor.; Reporter's Comments: This case concerns a 65-year-old, male subject with medical history of hypertension, diabetes mellitus type II and hypercholesterolemia, among others, and recent event of myocardial infarction, who experienced the unexpected event of acute pericarditis. The event occurred 3 months 9 days after the first dose of blinded study vaccine administration and 2 months 12 days after the last dose administration. The event, acute pericarditis, was reported as resolved. The event was considered unrelated to the study vaccine in agreement with the Investigator's assessment, noting the proximate event of myocardial infarction as a potential risk factor.