This spontaneous case was reported by a consumer and describes the occurrence of RHEUMATOID ARTHRITIS (Rheumatoid arthritis Flares in left knee/Leg) in a 53-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. Co-suspect product included non-company product ADALIMUMAB (HUMIRA) for Rheumatoid arthritis. Concurrent medical conditions included Rheumatoid arthritis. On an unknown date, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) 1 dosage form and ADALIMUMAB (HUMIRA) (Subcutaneous) at an unspecified dose. On 22-Nov-2021, the patient experienced RHEUMATOID ARTHRITIS (Rheumatoid arthritis Flares in left knee/Leg) (seriousness criterion medically significant). On an unknown date, the patient experienced GAIT INABILITY (Unable to walk), IMPAIRED WORK ABILITY (Inability to work) and PYREXIA (Fever). At the time of the report, RHEUMATOID ARTHRITIS (Rheumatoid arthritis Flares in left knee/Leg) had not resolved, GAIT INABILITY (Unable to walk) and IMPAIRED WORK ABILITY (Inability to work) outcome was unknown and PYREXIA (Fever) had resolved. The action taken with mRNA-1273 (Moderna COVID-19 Vaccine) (Unknown) was unknown. No Concomitant medication reported. There was no reported medical history. It was unknown if patient was enrolled in a COVID-19 Vaccine Trial. The reporter's causality for the event(s) of RHEUMATOID ARTHRITIS FLARES IN LEFT KNEE/LEG, When leg Flared up Could not walk or work onset 22 Nov 2021, FEVER  as reaction to covid-19 vaccine, RHEUMATOID ARTHRITIS FLARES IN LEFT WRIST, RHEUMATOID ARTHRITIS FLARES IN LEFT KNEE/LEG, WHEN LEG FLARED UP COULD NOT WALK OR WORK unknown onset and RHEUMATOID ARTHRITIS FLARES IN LEFT KNEE/LEG, WHEN LEG FLARED UP could not walk or work unknown onset was not provided. 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. No Treatment medication reported. Company Comment: This is a spontaneous case concerning a 53-year-old female patient with medical history of rheumatoid arthritis, who experienced the unexpected, serious (medically significant) adverse event of special interest of Rheumatoid arthritis (Rheumatoid arthritis Flares), after receiving the first dose of mRNA-1273 vaccine. Exact date of vaccination, clinical course, diagnostic tests and further treatment details were not provided in the case. The event had not resolved at the time of the report. Medical history of rheumatoid arthritis remains a risk factor for the event. The benefit-risk relationship of mRNA-1273 is not affected by this report. Reporter did not allow further contact. Sender's Comments: This is a spontaneous case concerning a 53-year-old female patient with medical history of rheumatoid arthritis, who experienced the unexpected, serious (medically significant) adverse event of special interest of Rheumatoid arthritis (Rheumatoid arthritis Flares), after receiving the first dose of mRNA-1273 vaccine. Exact date of vaccination, clinical course, diagnostic tests and further treatment details were not provided in the case. The event had not resolved at the time of the report. Medical history of rheumatoid arthritis remains a risk factor for the event. The benefit-risk relationship of mRNA-1273 is not affected by this report.