After the first booster diarrhea continued but did not get worst/ diarrhea on and off; A-FIB after first booster vaccine; COVID disease after first booster/2nd COVID disease after first booster/mild COVID symptoms after 2nd COVID disease after first booster; This spontaneous case was reported by a consumer and describes the occurrence of ATRIAL FIBRILLATION (A-FIB after first booster vaccine) in a 75-year-old male patient who received mRNA-1273 (Moderna COVID-19 Vaccine) for COVID-19 vaccination. The occurrence of additional non-serious events is detailed below.     The patient's past medical history included Cataract operation in December 2021 and Cataract operation in January 2022. Concurrent medical conditions included Type II diabetes mellitus (No Medications).   In March 2021, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) 1 dosage form. In April 2021, received second dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) dosage was changed to 1 dosage form. In 2021, received third dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) dosage was changed to 1 dosage form. In November 2021, the patient experienced COVID-19 (COVID disease after first booster/2nd COVID disease after first booster/mild COVID symptoms after 2nd COVID disease after first booster). In January 2022, the patient experienced ATRIAL FIBRILLATION (A-FIB after first booster vaccine) (seriousness criterion medically significant). On an unknown date, the patient experienced DIARRHOEA (After the first booster diarrhea continued but did not get worst/ diarrhea on and off). The patient was treated with APIXABAN (ELIQUIS) for AFib, at an unspecified dose and frequency and METOPROLOL for AFib, at an unspecified dose and frequency. At the time of the report, ATRIAL FIBRILLATION (A-FIB after first booster vaccine) and COVID-19 (COVID disease after first booster/2nd COVID disease after first booster/mild COVID symptoms after 2nd COVID disease after first booster) outcome was unknown and DIARRHOEA (After the first booster diarrhea continued but did not get worst/ diarrhea on and off) had not resolved.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): In November 2021, SARS-CoV-2 test: positive (Positive) Positive. In 2022, SARS-CoV-2 test: positive (Positive) Positive.         Concomitant product use was not provided by the reporter.  Patient had COVID disease twice. In Nov-2021 with breathing problems and in Jan or Feb-2022 with mild symptoms.  Patient had cataract surgery in Dec-2021 and Jan-2022.  Patient also had shingles shot and pneumonia vaccine at the end of 2021 and beginning of 2022. Patient did not remember the exact dates.   Doctor referred the patient to a gastroenterologist but the patient did not make a follow-up appointment with gastroenterologist.  Patient received cataract surgery eye drops in Dec-2021 and Jan-2022.  CC:This spontaneous case concerns a 75-year-old male patient, with no relevant history reported, who experienced the unexpected, serious (medically significant) events of Atrial fibrillation (AESI) and COVID-19 (AESI), which occurred unknown days after the third (booster) dose of mRNA-1273 vaccine administration. The outcome of the events was reported as unknown. The ongoing COVID-19 pandemic and the patient's age could be confounders for the events. The benefit-risk relationship of mRNA-1273 vaccine is not affected by this report.   This case was linked to MOD-2022-558756, MOD-2022-558762 (Patient Link).   Reporter did not allow further contact; Sender's Comments: This spontaneous case concerns a 75-year-old male patient, with no relevant history reported, who experienced the unexpected, serious (medically significant) events of Atrial fibrillation (AESI) and COVID-19 (AESI), which occurred unknown days after the third (booster) dose of mRNA-1273 vaccine administration. The outcome of the events was reported as unknown. The ongoing COVID-19 pandemic and the patient's age could be confounders for the events. The benefit-risk relationship of mRNA-1273 vaccine is not affected by this report.