Covid-19; Atrial Fibrillation after first and second dose of vaccine; This spontaneous case was reported by a consumer and describes the occurrence of ATRIAL FIBRILLATION (Atrial Fibrillation after first and second dose of vaccine) in a 78-year-old female patient who received mRNA-1273 (Spikevax) for COVID-19 prophylaxis. The occurrence of additional non-serious events is detailed below.     Concurrent medical conditions included Atrial fibrillation (for several years, since Childhood).   On 08-Feb-2022, the patient received first dose of mRNA-1273 (Spikevax) (unknown route) 1 dosage form. In 2022, received second dose of mRNA-1273 (Spikevax) (unknown route) dosage was changed to 1 dosage form. In 2022, the patient experienced ATRIAL FIBRILLATION (Atrial Fibrillation after first and second dose of vaccine) (seriousness criterion medically significant). On 01-Oct-2022, the patient experienced COVID-19 (Covid-19). At the time of the report, ATRIAL FIBRILLATION (Atrial Fibrillation after first and second dose of vaccine) and COVID-19 (Covid-19) outcome was unknown.        For mRNA-1273 (Spikevax) (Unknown), the reporter did not provide any causality assessments.   No concomitant product was reported. No treatment information was reported.  The patient received his Moderna primary series and two monovalent booster doses. Patient had Covid-19 infection in early October. Patient tested positive for Covid-19 on October 1, 2022. After first two Moderna primary series vaccines she had Atrial fibrillation. She did not have any adverse reactions after her booster doses. Her Doctor told her that this is likely because the booster dose is half the dose of the primary series dose. she had a history of Atrial Fibrillation since Childhood. she received my first dose of the Moderna Covid-19 vaccine on February 8, 2022 (Unfortunately the following information due to a computer issue was lost. Lot numbers on other vaccines was lost to follow up) The patient was admitted to the hospital for the Atrial Fibrillation after his first and second Moderna Covid-19 vaccine booster dose. The patient naturally converted out of Atrial Fibrillation after the first booster dose. After the second booster dose the patient had to have a cardioversion performed to convert back to normal rhythm.  Company comment- This spontaneous case concerns a 78-year-old female patient with relevant medical history of atrial fibrillation, who experienced unexpected, serious (medically significant) AESI Atrial fibrillation, which occurred at an unknown time with regards to the vaccination with a second dose of mRNA-1273. The patient reported that after her first moderna two primary series vaccines, the patient had atrial fibrillation. The outcome of the events was reported as unknown. The relevant medical history of atrial fibrillation is a risk factor for the event. The benefit-risk relationship of mRNA-1273 vaccine is not affected by this report.   This case was linked to MOD-2022-687872 (Patient Link).; Sender's Comments: This spontaneous case concerns a 78-year-old female patient with relevant medical history of atrial fibrillation, who experienced unexpected, serious (medically significant) AESI Atrial fibrillation, which occurred at an unknown time with regards to the vaccination with a second dose of mRNA-1273. The patient reported that after her first moderna two primary series vaccines, the patient had atrial fibrillation. The outcome of the events was reported as unknown. The relevant medical history of atrial fibrillation is a risk factor for the event. The benefit-risk relationship of mRNA-1273 vaccine is not affected by this report.