Diagnosed with A-Fib after first shot; Swollen Feet after first shot; Tired after first shot; This spontaneous case was reported by a patient family member or friend and describes the occurrence of ATRIAL FIBRILLATION (Diagnosed with A-Fib after first shot) and PERIPHERAL SWELLING (Swollen Feet after first shot) in a 70-year-old male patient who received mRNA-1273 (Moderna COVID-19 Vaccine) (batch no. 004M20A) for COVID-19 vaccination. The occurrence of additional non-serious events is detailed below.     No Medical History information was reported.    On 27-Jan-2021, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) 1 dosage form. In February 2021, the patient experienced ATRIAL FIBRILLATION (Diagnosed with A-Fib after first shot) (seriousness criteria hospitalization and medically significant) and PERIPHERAL SWELLING (Swollen Feet after first shot) (seriousness criterion hospitalization). On an unknown date, the patient experienced FATIGUE (Tired after first shot). The patient was hospitalized for 3 days due to ATRIAL FIBRILLATION and PERIPHERAL SWELLING. At the time of the report, ATRIAL FIBRILLATION (Diagnosed with A-Fib after first shot) and PERIPHERAL SWELLING (Swollen Feet after first shot) outcome was unknown and FATIGUE (Tired after first shot) had resolved.        mRNA-1273 (Moderna COVID-19 Vaccine) (Unknown) dosing remained unchanged.       Concomitant medication was not reported. Treatment information was not reported.  For mRNA-1273 (COVID 19 Vaccine) (unknown route), the reporter did not provide any causality assessments.  After first vaccine, the patient was tired for a few days. Right before the 2nd shot, his feet were swollen. Visited ER, and he was diagnosed with A-Fib. The patient was kept him in the hospital for 3 days. MD said to go ahead with second shot.  Company comment:  This case concerns a 70-year-old male patient with no medical history provided, who experienced the serious unexpected event of Atrial fibrillation (AESI) and Peripheral swelling, as well as non-serious expected event of Fatigue. Reportedly, the patient was feeing tired after first vaccination with mRNA-1273 vaccine, but the exact start date was not provided. In addition, right before the second vaccination, the patient's feet were swollen (Peripheral swelling) and he visited emergency department where he was diagnosed with atrial fibrillation and the patient was kept in the hospital for 3 days. The outcome of the events of Atrial fibrillation and Peripheral swelling remained unknown, while the event of Fatigue had resolved. The re-challenge for the event of Fatigue is considered positive as it was stated that the same event occurred after the second dose, as well. The re-challenge for the remaining two events cannot be determined as the outcome of the events was not specified. The patient's elderly age is considered as a risk factor for the reported events. The benefit-risk relationship of the mRNA-1273 vaccine is not affected by this report.   This case was linked to MOD-2021-400052 (Patient Link).; Sender's Comments: This case concerns a 70-year-old male patient with no medical history provided, who experienced the serious unexpected event of Atrial fibrillation (AESI) and Peripheral swelling, as well as non-serious expected event of Fatigue. Reportedly, the patient was feeing tired after first vaccination with mRNA-1273 vaccine, but the exact start date was not provided. In addition, right before the second vaccination, the patient's feet were swollen (Peripheral swelling) and he visited emergency department where he was diagnosed with atrial fibrillation and the patient was kept in the hospital for 3 days. The outcome of the events of Atrial fibrillation and Peripheral swelling remained unknown, while the event of Fatigue had resolved. The re-challenge for the event of Fatigue is considered positive as it was stated that the same event occurred after the second dose, as well. The re-challenge for the remaining two events cannot be determined as the outcome of the events was not specified. The patient's elderly age is considered as a risk factor for the reported events. The benefit-risk relationship of the mRNA-1273 vaccine is not affected by this report.