Feels like she is going nuts; severe joint stiffness, even in fingers; This is a spontaneous report received from a contactable reporter (Consumer or other non-HCP). The reporter is the patient.  A 71-year-old female patient received bnt162b2 omi xbb.1.5 (COMIRNATY (2023-2024 FORMULA)), on 11Nov2023 as DOSE 1, 0.3 mL SINGLE (lot number: CHG5967, expiration date: 25Dec2023) at the age of 71 years, administered in the left arm, for COVID-19 immunization. The patient's relevant medical history included: "Suspected lung cancer" (unspecified if ongoing), notes: May have lung cancer. Getting second scan; "Has lung nodules" (unspecified if ongoing), notes: They are not sure. Has no symptoms. Concomitant medication(s) included: INFLUENZA VACCINE taken for immunization, on 18Oct2023 as dose number unknown, single. Vaccination history included: Comirnaty (first dose, administered in the left arm (lot number: EL1283) as DOSE 1, SINGLE), administration date: 09Jan2021, when the patient was 68 years old, for COVID-19 immunization; Comirnaty (second dose, administered in the left arm (lot number: EN5318) as DOSE 2, SINGLE), administration date: 29Jan2021, when the patient was 68 years old, for COVID-19 immunization; Comirnaty (third dose, administered in the left arm (lot number: FF2589) as DOSE 3 (BOOSTER), SINGLE), administration date: 01Oct2021, when the patient was 69 years old, for COVID-19 immunization; Comirnaty (fourth dose, administered in the left arm (lot number: FP7135) as DOSE 4 (BOOSTER), SINGLE), administration date: 09Jun2022, when the patient was 69 years old, for COVID-19 immunization; Comirnaty (fifth dose, administered in the left arm (lot number: GJ3277) as DOSE 5 (BOOSTER), SINGLE), administration date: 23Sep2022, when the patient was 70 years old, for COVID-19 immunization. The following information was reported: JOINT STIFFNESS (non-serious) with onset 15Nov2023, outcome "not recovered" described as "severe joint stiffness, even in fingers"; FEELING ABNORMAL (non-serious), outcome "unknown" described as "Feels like she is going nuts." Relevant laboratory tests and procedures are available in the appropriate section. Therapeutic measures were taken as a result of joint stiffness.  Additional information: Patient called to ask a question regarding the latest Covid booster, from Pfizer. She got the booster on 11Nov2023. All of a sudden, since last Wednesday, 15Nov2023, she had such severe joint stiffness, even in fingers. Seems like someone took a baseball bat to the knee. Has anyone reported that side effect? Feels like she is going nuts. Patient clarified, after getting Pfizer Covid booster on 11Nov2023, the severe joint stiffness started 15Nov2023. The event has stayed the same, is pretty bad. She has taken Tylenol Arthritis, Ibuprofen, that helps but immediately after, it wears off, it comes back. The events did not require visit to hospital; patient stated "No, hopes not." This Pfizer Covid booster, 12 plus is like her sixth one. She had them all, the Covid vaccines. Arm is fine, that part is not even hurting. She is over 65 and going away on trip this week, that is why she got vaccinated. She also got flu shot 2 weeks before, later clarified as "before 4 weeks prior to latest Pfizer Covid booster." Thinking, she better get this. When asked about test results, she stated "not really, all test results, blood work, everything has been good." Patient's medical history was reported as "May have lung cancer. Getting second scan tomorrow. Has lung nodules, they are not sure, has no symptoms." Family medical history relevant to adverse events was reported as "No, husband has same thing, is fine."; Sender's Comments: Linked Report(s) : US-PFIZER INC-202300396867 same patient, different vaccine dose and event;