went into a fib; couldn't eat; was throwing up; This spontaneous case was reported by a patient family member or friend and describes the occurrence of ATRIAL FIBRILLATION (went into a fib) in a 69-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 Motor vehicle accident (Car accident) in 2007, Fibrillation atrial (He had ablation in 2014, which took away the a fib.) and Cardiac ablation in 2014.   On 24-Mar-2021, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) 1 dosage form. On 14-Apr-2021, received second dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) dosage was changed to 1 dosage form. On 23-Oct-2021, received third dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) dosage was changed to 1 dosage form. On 13-May-2022, received fourth dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) dosage was changed to 1 dosage form. On 14-May-2022, the patient experienced DECREASED APPETITE (couldn't eat) and VOMITING (was throwing up). On 16-May-2022, the patient experienced ATRIAL FIBRILLATION (went into a fib) (seriousness criterion medically significant). At the time of the report, ATRIAL FIBRILLATION (went into a fib) outcome was unknown and DECREASED APPETITE (couldn't eat) and VOMITING (was throwing up) was resolving.            No concomitant medication was reported.  On 15-May-2022, patient felt better.  Patient  was on unspecified medication and blood thinners.  Company Comment:  This spontaneous case concerns a 69-year-old male patient with relevant medical history of Fibrillation atrial (with ablation in 2014), who experienced the unexpected serious (medically significant) adverse event of special interest Atrial fibrillation, that occurred 3 days after receiving 2nd booster of mRNA-1273 vaccine as 4th dose in the vaccination series.  Patient presented with vomiting and loss of appetite the day after vaccination and felt better the next day. However, on the third day of vaccination, patient went into atrial fibrillation and was treated with unspecified medications and blood thinners. Patient previously received 3 doses of mRNA-1273 vaccines consisting of a 2-dose primary series given 21 days apart, and a third dose as 1st booster given 6 months and 20 days prior to current mRNA-1273 vaccine. Recurrence of atrial fibrillation after catheter ablation remains common especially in the presence of risk factors such as a possible electrolyte imbalance that could have been caused by the vomiting of the patient. The benefit-risk relationship of mRNA-1273 Vaccine is not affected by this report.   This case was linked to MOD-2022-573547.; Sender's Comments: This spontaneous case concerns a 69-year-old male patient with relevant medical history of Fibrillation atrial (with ablation in 2014), who experienced the unexpected serious (medically significant) adverse event of special interest Atrial fibrillation, that occurred 3 days after receiving 2nd booster of mRNA-1273 vaccine as 4th dose in the vaccination series.  Patient presented with vomiting and loss of appetite the day after vaccination and felt better the next day. However, on the third day of vaccination, patient went into atrial fibrillation and was treated with unspecified medications and blood thinners. Patient previously received 3 doses of mRNA-1273 vaccines consisting of a 2-dose primary series given 21 days apart, and a third dose as 1st booster given 6 months and 20 days prior to current mRNA-1273 vaccine. Recurrence of atrial fibrillation after catheter ablation remains common especially in the presence of risk factors such as a possible electrolyte imbalance that could have been caused by the vomiting of the patient. The benefit-risk relationship of mRNA-1273 Vaccine is not affected by this report.