Undifferentiated polyarthritis; synovitis; This is a report for the following:  A 66-year-old female patient received BNT162b2 (BNT162B2), as dose 2, single (Batch/Lot number: unknown) for covid-19 immunisation. The patient's relevant medical history and concomitant medications were not reported. Vaccination history included: Pfizer-biontech (DOSE 1, SINGLE), for Covid-19 immunization. The following information was reported: POLYARTHRITIS (medically significant), 1 day after the suspect product(s) administration, outcome "recovering", described as "Undifferentiated polyarthritis"; SYNOVITIS (medically significant), outcome "recovering". The patient underwent the following laboratory tests and procedures: Antibody test: negative; Antinuclear antibody: negative; Computerised tomogram abdomen: negative, notes: for occult malignancy; Computerised tomogram pelvis: negative, notes: for occult malignancy; Computerised tomogram thorax: negative, notes: for occult malignancy; C-reactive protein: 22.7 mg/dl; Haemoglobin: 9.9 g/dl, notes: normocytic anemia; Hepatitis B virus test: negative; Hepatitis C virus test: negative; HIV test: negative; Examination: remarkable for synovitis of the bilateral knees, notes: ankles; Platelet count: 548, notes: unit: x10^3; Positron emission tomogram: remarkable for uptake in the left second and, notes: right second and third MTP joints; Red blood cell sedimentation rate: greater than 120, notes: unit: mm/h elevated; Rheumatoid factor: negative; SARS-CoV-2 test: negative; Serum ferritin (15-150): 1820 ng/ml; Treponema test: negative; White blood cell count: 16310 /mm3, notes: leukocytosis; X-ray: negative, notes: for chondrocalcinosis. Therapeutic measures were taken as a result of polyarthritis, synovitis.  Clinical information: A 66-year-old woman presented to rheumatology with 2 months of symmetric polyarthritis involving her knees, ankles, and MTP joints in the setting of low-grade fever and chills. Symptom onset occurred 1 day after completing the Pfizer-BioNTech vaccination series. The patient had no personal or family history of autoimmune disease and no history of COVID infection. The patient never received immunosuppression in the past, and no medication changes were made at the time of vaccination. Examination was remarkable for synovitis of the bilateral knees and ankles, which improved after a 2-week course of indomethacin. Laboratory evaluation was remarkable for a leukocytosis (16,310/ microliter), normocytic anemia (9.9 g/dL), and thrombocytosis (548 x 103), as well as an elevated ESR (>120 mm/h), CRP (22.7 mg/dL), and ferritin (1820 ng/mL; reference range, 15 -150 ng/mL). FANA test, RF, ACPA, HBV, HCV, HIV, rapid plasma reagin test, and COVID-19 testing (PCR) were negative. Radiographic survey was negative for chondrocalcinosis, and the patient did not meet the criteria for adult-onset Still disease. A contrasted computed tomography scan of the chest, abdomen, and pelvis was negative for occult malignancy. Subsequent positron emission tomography/computed tomography was remarkable for uptake in the left second and right second and third MTP joints. The patient was diagnosed as having undifferentiated polyarthritis and continued indomethacin for another 4 weeks before transitioning to ibuprofen as needed. At the 4-month interval, her synovitis had improved, but her inflammatory markers took 2 more months to resolve.; Sender's Comments: As there is limited information in the case provided, the causal association between the reported events: "Polyarthritis", "Synovitis" and the suspect drug BNT162B2 cannot be excluded. The case will be reassessed once new information is available.   The impact of this report on the benefit/risk profile of the Pfizer drug is evaluated as part of Pfizer procedures for safety evaluation, including the review and analysis of aggregate data for adverse events. Any safety concern identified as part of this review, as well as any appropriate action in response, will be promptly notified to Regulatory Authorities, Ethics Committees and Investigators, as appropriate.