booster; I CAN BARELY WALK MOST DAYS.; Pain not diminishing at all; Serious brain fog never had before; Old sacroiliac hip injury and sciatica flared up immediately after each injection; Old sacroiliac hip injury and sciatica flared up immediately after each injection; Old sacroiliac hip injury and sciatica flared up immediately after each injection; This is a spontaneous report received from a contactable reporter (Consumer or other non-HCP). The reporter is the patient.  A 68-year-old female patient (not pregnant) received BNT162B2 (PFIZER-BIONTECH COVID-19 VACCINE), administered in arm left, administration date 05Oct2021 (Lot number: FE3590) at the age of 68 years as dose 3 (booster), single for COVID-19 immunisation. Relevant medical history included: "hypothyroid" (unspecified if ongoing); "sacroiliitis" (unspecified if ongoing), notes: for 3 years; "sciatica" (unspecified if ongoing), notes: for 11 years; "old sacroiliac hip injury" (unspecified if ongoing). There were no concomitant medications. Past drug history included: Statins, reaction: "drug allergy". Vaccination history included: BNT162B2 (Dose 1, single), administration date: 05Mar2021, for COVID-19 immunization, reaction(s): "Old sacroiliac hip injury and sciatica flared up immediately after each injection"; BNT162B2 (Dose 2, single), administration date: 01Apr2021, when the patient was 68 years old, for COVID-19 immunization, reaction(s): "Old sacroiliac hip injury and sciatica flared up immediately after each injection". The following information was reported: IMMUNISATION (disability) with onset 05Oct2021, outcome "unknown", described as "booster"; GAIT INABILITY (disability) with onset 05Oct2021, outcome "not recovered", described as "I CAN BARELY WALK MOST DAYS."; PAIN (disability) with onset 05Oct2021, outcome "not recovered", described as "Pain not diminishing at all"; FEELING ABNORMAL (disability) with onset 05Oct2021, outcome "not recovered", described as "Serious brain fog never had before"; JOINT INJURY (disability), SCIATICA (disability), CONDITION AGGRAVATED (disability) all with onset 05Oct2021, outcome "not recovered" and all described as "Old sacroiliac hip injury and sciatica flared up immediately after each injection". Therapeutic measures were not taken as a result of gait inability, pain, feeling abnormal, joint injury, sciatica, condition aggravated. Clinical course details: Patient had no COVID prior to vaccination and had not tested positive post vaccination. Patient reported old sacroiliac hip injury and sciatica flared up immediately after each injection-inflammation. This faded after first vaccination after a couple of days then after second vaccination in a week, with third vaccine, patient can barely walk most days. Serious brain fog never had before. Almost 3 months of pain and brain fog after third vaccine. Pain not diminishing at all as of 01Jan2022. Cannot function in my life. Definitely related to vaccine. Patient did not have flare ups in these areas for years.  Pain started the day of each injection. Serious side effects. Exercises and diet that helped in the past did not work.   Follow-up attempts are completed. No further information is expected.