This literature-non-study case was reported in a literature article and describes the occurrence of ATRIAL FIBRILLATION (Atrial fibrillation) and SYNCOPE (Syncope) in a 20-year-old female patient who received mRNA-1273 (Spikevax) for COVID-19 vaccination. The occurrence of additional non-serious events is detailed below. LITERATURE REFERENCE: New atrial fibrillation and syncope in a collegiate athlete immediately following COVID-19 vaccination. 2022;79(9 Supplement):2326. No Medical History information was reported. On an unknown date, the patient received first dose of mRNA-1273 (Spikevax) (unknown route) 1 dosage form. On an unknown date, the patient experienced ATRIAL FIBRILLATION (Atrial fibrillation) (seriousness criterion medically significant), SYNCOPE (Syncope) (seriousness criterion medically significant) and INTENTIONAL DOSE OMISSION (the patient declined the second dose). At the time of the report, ATRIAL FIBRILLATION (Atrial fibrillation), SYNCOPE (Syncope) and INTENTIONAL DOSE OMISSION (the patient declined the second dose) outcome was unknown. Related. DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On an unknown date, Blood iron: normal (normal) Normal. On an unknown date, Blood thyroid stimulating hormone: normal (normal) Normal. On an unknown date, Cardiac electrophysiologic study: no accessory pathway, though AF with RVR recurred no accessory pathway, though AF with RVR recurred during her EPS and required electrical cardioversion. On an unknown date, Cardiopulmonary exercise test: above average peak rate of oxygen uptake(vo2) of 4 revealed above average peak rate of oxygen uptake(VO2) of 48.1 ml/kg/min (134% predicted), appropriate cardiopulmonary response to exercise, and no ECG changes. On an unknown date, Full blood count: normal (normal) Normal. On an unknown date, Myocardial necrosis marker: normal (normal) Normal. On an unknown date, Sinus rhythm: AF with rapid ventricular response (RVR) at 150 BEA AF with rapid ventricular response (RVR) at 150 beats per minute. mRNA-1273 (Spikevax) (Unknown) was withdrawn on an unknown date. For mRNA-1273 (Spikevax) (Unknown), the reporter considered ATRIAL FIBRILLATION (Atrial fibrillation), SYNCOPE (Syncope) and INTENTIONAL DOSE OMISSION (the patient declined the second dose) to be related. No concomitant and treatment medications were reported. Patient was reported to be a collegiate long distance runner with no medical history presented with palpitations and syncope 15 minutes after receiving Moderna COVID-19 vaccine dose 1. Patient spontaneously cardioverted to normal sinus rhythm (NSR) shortly thereafter, though developed prolonged exertional intolerance for several months. 2-week ambulatory rhythm monitoring showed NSR with no recurrent AF. Patient was advised a graded exercise protocol for return to sports participation. Company comment: This literature non-study case concerns a 20  year  old, female athlete patient, who experienced the unexpected, serious medically significant AESI of atrial fibrillation, and the unexpected serious medically significant event of syncope. The events occurred the same days after the administration of the first dose of mRNA-1273 vaccine. The review stated that the patient experienced palpitations and syncope 15 minutes after vaccination. The initial rhythm was atrial fibrillation with rapid ventricular response at 150 beats per minute. She spontaneously cardioverted to normal sinus rhythm in a short period of time; however, she developed prolonged exertional intolerance for several months. In an electrophysiological study the atrial fibrillation recurred and required electrical cardioversion. After this, a 2  week ambulatory rhythm monitoring showed normal sinus rhythm with no longer recurrence of atrial fibrillation. A cardiopulmonary stress test revealed above average peak rate of oxygen uptake. Patient´s athletic condition (collegiate long  distance runner) remains as confounder for atrial fibrillation. The benefit-risk relationship of mRNA-1273 vaccine is not affected by this report. Sender's Comments: This literature non-study case concerns a 20  year  old, female athlete patient, who experienced the unexpected, serious medically significant AESI of atrial fibrillation, and the unexpected serious medically significant event of syncope. The events occurred the same days after the administration of the first dose of mRNA-1273 vaccine. The review stated that the patient experienced palpitations and syncope 15 minutes after vaccination. The initial rhythm was atrial fibrillation with rapid ventricular response at 150 beats per minute. She spontaneously cardioverted to normal sinus rhythm in a short period of time; however, she developed prolonged exertional intolerance for several months. In an electrophysiological study the atrial fibrillation recurred and required electrical cardioversion. After this, a 2  week ambulatory rhythm monitoring showed normal sinus rhythm with no longer recurrence of atrial fibrillation. A cardiopulmonary stress test revealed above average peak rate of oxygen uptake. Patient´s athletic condition (collegiate long  distance runner) remains as confounder for atrial fibrillation. The benefit-risk relationship of mRNA-1273 vaccine is not affected by this report.