increase in A-FIB; Fever of 102.5; severe chills; Interchange of vaccine products; This is a spontaneous report received from a contactable reporter (Other HCP). The reporter is the patient.  A 65-year-old female patient (not pregnant) received BNT162b2, BNT162b2 omi ba.4-5 (BNT162B2, BNT162B2 OMI BA.4-5), on 08Oct2022 at 11:15 as dose 4 (booster), single (Lot number: RIA11020) at the age of 65 years, in left arm for covid-19 immunisation. The patient's relevant medical history included: "Heart Failure" (unspecified if ongoing), notes: Other medical history: Heart Failure; "A-Fib" (unspecified if ongoing), notes: Other medical history: A-Fib; "Valvular heart disease" (unspecified if ongoing), notes: Valvular heart disease With replacement heart valves and Pacemaker; "heart disease With replacement heart valves" (unspecified if ongoing), notes: Valvular heart disease With replacement heart valves and Pacemaker. The patient took concomitant medications. Past drug history included: Floroquinolones, reaction(s): "Known allergies: floroquinolones", notes: Known allergies: floroquinolones. Vaccination history included: moderna (Dose Number: 3, Batch/Lot No: 058F21, Location of injection: Arm Left, Vaccine Administration Time: 01:15 PM), administration date: 08Nov2021, when the patient was 64-year-old, for Covid-19 Immunization; moderna (Dose Number: 2, Batch/Lot No: 030M20A, Location of injection: Arm Left, Vaccine Administration Time: 03:15 PM), administration date: 04Feb2021, when the patient was 64-year-old, for Covid-19 Immunization; moderna (Dose Number: 1, Batch/Lot No: 026620A, Location of injection: Arm Left, Vaccine Administration Time: 09:45 AM), administration date: 05Jan2021, when the patient was 63-year-old, for Covid-19 Immunization. The following information was reported: INTERCHANGE OF VACCINE PRODUCTS (medically significant) with onset 08Oct2022 at 11:15, outcome "unknown"; PYREXIA (medically significant) with onset 09Oct2022 at 04:00, outcome "not recovered", described as "Fever of 102.5"; ATRIAL FIBRILLATION (medically significant) with onset 09Oct2022 at 04:00, outcome "not recovered", described as "increase in A-FIB"; CHILLS (medically significant) with onset 09Oct2022 at 04:00, outcome "not recovered", described as "severe chills". The patient underwent the following laboratory tests and procedures: Body temperature: (09Oct2022) 102.5, notes: Fever of 102.5. Therapeutic measures were not taken as a result of atrial fibrillation, pyrexia, chills.  Clinical course: No other vaccine in four weeks; had other medications in two weeks. Patient did not have Covid prior to vaccination. Patient was not tested for Covid post vaccination.; Sender's Comments: A contributory role of BNT162B2 to events increase in A-FIB, fever of 102.5, severe chills cannot be excluded based on temporal association and available information. The impact of this report on the benefit/risk profile of the Pfizer product 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.