appendicitis; Interchange of vaccine products; weakness; not feeling good began; fever; This is a spontaneous report received from contactable reporter(s) (Nurse) from medical information team.  A 79-year-old male patient received BNT162b2, BNT162b2 omi ba.4-5 (BNT162B2, BNT162B2 OMI BA.4-5), on 07Oct2022 as dose 5 (booster), 0.3 ml single (Lot number: GJ2524, Expiration Date: 30Jun2023) at the age of 79 years intramuscular, in left deltoid for covid-19 immunisation. The patient's relevant medical history included: "Cerebral infarction" (unspecified if ongoing); "Traumatic brain injury" (unspecified if ongoing); "Dementia" (unspecified if ongoing); "Diabetes type 2" (unspecified if ongoing), notes: Diabetes type 2; "Major depressive disorder" (unspecified if ongoing), notes: Major depressive disorder; "patient is flaccid on the left side" (unspecified if ongoing), notes: age related physical disability Caller clarified that the patient is flaccid on the left side; "right humerus bone fracture" (unspecified if ongoing), notes: right humerus bone fracture this was a couple years ago; "Obsessive-compulsive disorder" (unspecified if ongoing). There were no concomitant medications. Vaccination history included: moderna (First Dose: Date 22JAN2021, Lot 027120A, Moderna Covid MRNA 0.5 IM), administration date: 22Jan2021, when the patient was 77-year-old, for Covid-19 immunization; moderna (Second Dose: Date 19FEB2021, Lot 010M20A), administration date: 19Feb2021, when the patient was 77-year-old, for Covid-19 immunization; moderna (Third dose: Date 05JAN2022, Lot 001J21-2A, Moderna), administration date: 05Jan2022, when the patient was 78-year-old, for Covid-19 immunization; moderna (Fourth dose: Date 14JUL2022, Lot 002M21A), administration date: 14Jul2022, when the patient was 79-year-old, for Covid-19 immunization. The following information was reported: INTERCHANGE OF VACCINE PRODUCTS (hospitalization, medically significant) with onset 07Oct2022, outcome "unknown"; PYREXIA (caused and prolonged hospitalization) with onset 07Oct2022, outcome "not recovered", described as "fever"; APPENDICITIS (hospitalization, medically significant) with onset 08Oct2022 at 04:30, outcome "unknown"; ASTHENIA (non-serious), outcome "unknown", described as "weakness"; MALAISE (non-serious), outcome "unknown", described as "not feeling good began". The patient was hospitalized for interchange of vaccine products, appendicitis (start date: 08Oct2022); for pyrexia (start date: 07Oct2022). The patient underwent the following laboratory tests and procedures: Body temperature: (07Oct2022) 104 Fahrenheit, notes: fever of 104 degrees Fahrenheit; Glycosylated haemoglobin: (29Aug2022) elevated, notes: Result: elevated; Unit: Not Provided. which was expected since he has diabetes, it is under 7. Therapeutic measures were taken as a result of appendicitis.  Clinical course: Caller states that she was calling about the Pfizer Bivalent Covid Booster, she doesn't know if this was indeed an adverse reaction but they had a patient that was given the bivalent vaccine on Friday morning 07Oct2022, then by the same evening had a fever of 104 degrees Fahrenheit. This patient was then hospitalized in which the patient was diagnosed with acute appendicitis and had an emergency appendectomy. Caller adds that she has gone through the information and saw that patient are at risk for appendicitis but that was only observed in 12 cases and 4 of them were placebo, so she does not know if this was considered an adverse reaction. The appendicitis was diagnosed early morning on the 08Oct2022, at 4:30AM, the appendectomy took place yesterday 08Oct2022. The Concomitant Medications were None, the patient was completely stable and himself, he was fine up until about 11 at night, that is when the weakness and not feeling good began.   No follow-up attempts are possible. No further information is expected.; Sender's Comments: Based on the temporal relation, the association between the events of appendicitis and pyrexia and the suspect product BNT162B2 cannot be completely ruled out.  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.