Flare up of arthritis; Back pain; Dehydration; Atrial fibrillation; Mobility decreased / DIFFICULTY STANDING UP AFTER PROLONGED SITTING; Ankle swelling; Knee swelling; This spontaneous case was reported by a consumer and describes the occurrence of ATRIAL FIBRILLATION (Atrial fibrillation) 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.    Co-suspect product included non-company product ADALIMUMAB (HUMIRA) solution for injection for Plaque psoriasis.    The patient had no known allergies.  The patient's past medical history included Psoriasis flare-up (recurrence of psoriasis) from 2020 to May 2021. Previously administered products included for Drug use for unknown indication: LISINOPRIL. Past adverse reactions to the above products included No adverse event with LISINOPRIL. Family history included Polyp (in colon) since an unknown date. Concurrent medical conditions included Blood pressure high since 2013, Alcohol use (up to 4 beers a day and unknown amount of vodka on weekends) and Plaque psoriasis. Concomitant products included METOPROLOL for Atrial fibrillation, AMLODIPINE and LOSARTAN for Blood pressure high, APIXABAN (ELIQUIS) for Blood viscosity abnormal.   On 01-Mar-2021, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) 1 dosage form. On 01-Apr-2021, received second dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) dosage was changed to 1 dosage form. On an unknown date, the patient started ADALIMUMAB (HUMIRA) (Subcutaneous) 40 mg,1 in 1 wk. In 2021, the patient experienced JOINT SWELLING (Knee swelling). In September 2021, the patient experienced JOINT SWELLING (Ankle swelling). In October 2021, the patient experienced ATRIAL FIBRILLATION (Atrial fibrillation) (seriousness criterion medically significant), MOBILITY DECREASED (Mobility decreased / DIFFICULTY STANDING UP AFTER PROLONGED SITTING) and DEHYDRATION (Dehydration). On 16-Nov-2021, the patient experienced BACK PAIN (Back pain). On an unknown date, the patient experienced ARTHRITIS (Flare up of arthritis). The patient was treated with TRAMADOL at an unspecified dose and frequency; PREDNISONE at an unspecified dose and frequency; APREMILAST (OTEZLA) at an unspecified dose and frequency; CORTISONE at an unspecified dose and frequency and INDOMETHACIN [INDOMETACIN] at an unspecified dose and frequency. In October 2021, ATRIAL FIBRILLATION (Atrial fibrillation) and DEHYDRATION (Dehydration) had resolved. On 17-Nov-2021, BACK PAIN (Back pain) had resolved. At the time of the report, ARTHRITIS (Flare up of arthritis) outcome was unknown and JOINT SWELLING (Knee swelling), MOBILITY DECREASED (Mobility decreased / DIFFICULTY STANDING UP AFTER PROLONGED SITTING) and JOINT SWELLING (Ankle swelling) had not resolved.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On an unknown date, Blood pressure measurement: HIGH BLOOD PRESSURE.    Company comment : This spontaneous case concerns a 69  year  old, male patient, with current condition of hypertension, in current treatment for atrial fibrillation (and anticoagulant therapy), plaque psoriasis in treatment with Adalimumab, and alcohol user, who experienced the serious (medically significant) unexpected AESI of atrial fibrillation, and the non  serious unexpected AESI of arthritis (described as "flare up arthritis"). Atrial fibrillation occurred approximately 6 months after the second dose of mRNA  1273 vaccine. Onset date of arthritis was not reported; hence latency and temporal association cannot be properly assessed. The outcome of atrial fibrillation was recovered. On unknown date and dose, the patient was treated with tramadol, prednisone, Apremilast, cortisone, and indomethacin. No further relevant clinical information was available for medical reviewing. Co-suspect product included Adalimumab, which is confounder for atrial fibrillation. Patient´s mentioned medical history (Psoriasis as confounding for cardiovascular disease, hypertension, with previous atrial fibrillation, and alcohol user) remains as risk factors for atrial fibrillation. Patient´s psoriasis remains as risk factor for arthritis. The benefit-risk relationship of mRNA-1273 vaccine is not affected by this report.     It was unknown if patient was enrolled in a COVID-19 Vaccine Trial.  The patient received HUMIRA(Solution for injection in pre-filled pen)(ADALIMUMAB).  The reporter's causality for the event(s) of knee swelling, difficulty standing up after prolonged sitting, ankle swelling, atrial fibrillation, flare up/recurrence of psoriasis, back pain, and dehydration with Humira 40mg/0.8ml(Adalimumab) was no reasonable possibility. The reporter's causality for the event(s) of flare up of arthritis with Humira 40mg/0.8ml(adalimumab) was a reasonable possibility.  This case was identified as part of a retrospective clean-up activity where certain emails received in the Moderna mailbox were missed to be booked in.     Reporter did not allow further contact; Sender's Comments: This spontaneous case concerns a 69  year  old, male patient, with current condition of hypertension, in current treatment for atrial fibrillation (and anticoagulant therapy), plaque psoriasis in treatment with Adalimumab, and alcohol user, who experienced the serious (medically significant) unexpected AESI of atrial fibrillation, and the non  serious unexpected AESI of arthritis (described as "flare up arthritis"). Atrial fibrillation occurred approximately 6 months after the second dose of mRNA  1273 vaccine. Onset date of arthritis was not reported; hence latency and temporal association cannot be properly assessed. The outcome of atrial fibrillation was recovered. On unknown date and dose, the patient was treated with tramadol, prednisone, Apremilast, cortisone, and indomethacin. No further relevant clinical information was available for medical reviewing. Co-suspect product included Adalimumab, which is confounder for atrial fibrillation. Patient´s mentioned medical history (Psoriasis as confounding for cardiovascular disease, hypertension, with previous atrial fibrillation, and alcohol user) remains as risk factors for atrial fibrillation. Patient´s psoriasis remains as risk factor for arthritis. The benefit-risk relationship of mRNA-1273 vaccine is not affected by this report.