admitted to the hospital for the Atrial Fibrillation after his first and second Moderna Covid-19 vaccine booster dose.; Vaccination failure; I tested positive for Covid-19 on October 1, 2022; This spontaneous case was reported by a consumer and describes the occurrence of ATRIAL FIBRILLATION (admitted to the hospital for the Atrial Fibrillation after his first and second Moderna Covid-19 vaccine booster dose.) in a 78-year-old female patient who received mRNA-1273 (Moderna COVID-19 Vaccine) for COVID-19 prophylaxis. The occurrence of additional non-serious events is detailed below.     The patient's past medical history included Cardioversion. Concurrent medical conditions included Atrial fibrillation (for several years, since Childhood.).   On an unknown date, the patient received fourth dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) 1 dosage form. On an unknown date, received third dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) dosage was changed to 1 dosage form. In 2022, the patient experienced ATRIAL FIBRILLATION (admitted to the hospital for the Atrial Fibrillation after his first and second Moderna Covid-19 vaccine booster dose.) (seriousness criteria hospitalization and medically significant). On 01-Oct-2022, the patient experienced COVID-19 (I tested positive for Covid-19 on October 1, 2022). On an unknown date, the patient experienced VACCINATION FAILURE (Vaccination failure). The patient was hospitalized on sometime in 2022 due to ATRIAL FIBRILLATION. In 2022, ATRIAL FIBRILLATION (admitted to the hospital for the Atrial Fibrillation after his first and second Moderna Covid-19 vaccine booster dose.) had resolved. At the time of the report, COVID-19 (I tested positive for Covid-19 on October 1, 2022) and VACCINATION FAILURE (Vaccination failure) outcome was unknown.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On 01-Oct-2022, SARS-CoV-2 test: Positive.     For mRNA-1273 (Moderna COVID-19 Vaccine) (Unknown), the reporter did not provide any causality assessments.   No concomitant information was reported.  The patient received Moderna primary series and two monovalent booster doses. Patient received first dose of the Moderna Covid-19 vaccine on 08-Feb-2022. Patient tested positive for Covid-19 on 1-Oct-2022. After first two Moderna primary series vaccines patient had Atrial fibrillation. 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.   This case was linked to MOD-2022-688105 (Patient Link).  Company comment: This is a spontaneous case, reported by a consumer, concerning a 78-year-old female patient with relevant medical condition of Atrial fibrillation since childhood, who experienced the unexpected serious (hospitalization and medically significant) adverse event of special interest Atrial fibrillation, in the context of the fourth dose of mRNA-1273 vaccine as the second booster dose of COVID-19 vaccine. Latency cannot be properly assessed since vaccination date nor the exact event onset date were provided. The patient received primary doses of mRNA-1273 vaccine and two monovalent booster doses of mRNA-1273 vaccination. It was reported that the patient had COVID-19 infection supported by a positive SARS-CoV-2 test, approximately 7 months and 3 weeks after the first dose of mRNA-1273 vaccine. Additionally, Vaccination failure was also reported. Patient also reported that after her first two Moderna primary series vaccines, patient had Atrial fibrillation and did not have any adverse reactions after the booster doses. The patient was admitted to the hospital for the Atrial Fibrillation and cardioversion was performed to convert back to normal rhythm. It was reported that the event Atrial fibrillation had resolved. The medical condition of Atrial fibrillation remains as a confounders for the event Atrial fibrillation. The benefit-risk relationship of mRNA-1273 is not affected by this report.; Sender's Comments: This is a spontaneous case, reported by a consumer, concerning a 78-year-old female patient with relevant medical condition of Atrial fibrillation since childhood, who experienced the unexpected serious (hospitalization and medically significant) adverse event of special interest Atrial fibrillation, in the context of the fourth dose of mRNA-1273 vaccine as the second booster dose of COVID-19 vaccine. Latency cannot be properly assessed since vaccination date nor the exact event onset date were provided. The patient received primary doses of mRNA-1273 vaccine and two monovalent booster doses of mRNA-1273 vaccination. It was reported that the patient had COVID-19 infection supported by a positive SARS-CoV-2 test, approximately 7 months and 3 weeks after the first dose of mRNA-1273 vaccine. Additionally, Vaccination failure was also reported. Patient also reported that after her first two Moderna primary series vaccines, patient had Atrial fibrillation and did not have any adverse reactions after the booster doses. The patient was admitted to the hospital for the Atrial Fibrillation and cardioversion was performed to convert back to normal rhythm. It was reported that the event Atrial fibrillation had resolved. The medical condition of Atrial fibrillation remains as a confounders for the event Atrial fibrillation. The benefit-risk relationship of mRNA-1273 is not affected by this report.