acute flare of CIDP leading to aspiration pneumonia; acute flare of CIDP leading to aspiration pneumonia; acute flare of CIDP leading to aspiration pneumonia; This is a literature report.  A 54-year-old male patient received BNT162b2, BNT162b2 omi ba.4-5 (BNT162B2, BNT162B2 OMI BA.4-5), as dose 4 (booster), single (Batch/Lot number: unknown) for covid-19 immunisation. The patient's relevant medical history included: "Chronic Inflammatory Demyelinating Polyneuropathy" (unspecified if ongoing); "Arnold Chiari syndrome type 2" (unspecified if ongoing); "hydrocephalus" (unspecified if ongoing); "spina bifida" (unspecified if ongoing); "neurogenic bladder" (unspecified if ongoing); "suprapubic catheter" (unspecified if ongoing); "recurrent urinary tract infection" (unspecified if ongoing); "chronic sacral ulcer" (unspecified if ongoing); "depression" (unspecified if ongoing); "obsessive-compulsive disorder" (unspecified if ongoing); "wheelchair-bound" (unspecified if ongoing), notes: Every 5-6 months; "noninvasive mechanical ventilation" (unspecified if ongoing). The patient's concomitant medications were not reported. Past drug history included: Immunoglobulin for CIDP exacerbation, notes: intravenous immunoglobulin (IVIG) 400. Vaccination history included: Bnt162b2 (DOSE 1, SINGLE), for COVID-19 immunisation; Bnt162b2 (DOSE 2, SINGLE), for COVID-19 immunisation; Bnt162b2, bnt162b2 omi ba.4-5 (DOSE 3 (BOOSTER), SINGLE), for COVID-19 immunisation, reaction(s): "CIDP exacerbation", "CIDP exacerbation". The following information was reported: CHRONIC INFLAMMATORY DEMYELINATING POLYRADICULONEUROPATHY (hospitalization, medically significant, life threatening), CONDITION AGGRAVATED (hospitalization, medically significant, life threatening), PNEUMONIA ASPIRATION (hospitalization, medically significant, life threatening), outcome "recovering" and all described as "acute flare of CIDP leading to aspiration pneumonia". The event "acute flare of cidp leading to aspiration pneumonia" required emergency room visit. The patient underwent the following laboratory tests and procedures: Alanine aminotransferase: 154; Aspartate aminotransferase: 160; Blood alkaline phosphatase: 353; Blood pressure measurement: within normal limits; 105/55; Body temperature: 102 Fahrenheit; Computerised tomogram: no evidence of intracranial hemorrhage, notes: territorial infarct or mass effect, chronic findings of Arnold Chiari malformation type 2 were seen, which were unchanged from the previous scan; Computerised tomogram abdomen: bilateral dependent lung, notes: dense consolidations and additional scattered patchy ground glass and consolidative opacities suspicious for aspiration pneumonia and osteomyelitis of the right ischial tuberosity underlying chronic sacral decubitus ulce; Computerised tomogram pelvis: bilateral dependent lung; Computerised tomogram thorax: bilateral dependent lung, notes: dense consolidations and additional scattered patchy ground glass and consolidative opacities suspicious for aspiration pneumonia and osteomyelitis of the right ischial tuberosity underlying chronic sacral decubitus ulce; Full blood count: normal; Heart rate: within normal limits; 154, notes: units:beats per minute; Electrodiagnostic: were consistent with severe multifocal, notes: demyelinating motor polyneuropathy with no signs to suggest superimposed myopathic polyneuropathy; 15, notes: units:cm of water; 76; Liver function test: normal; Magnetic resonance imaging: no acute changes; Metabolic function test: normal; Nerve conduction studies: were consistent with severe multifocal, notes: demyelinating motor polyneuropathy with no signs to suggest superimposed myopathic polyneuropathy; Neurological examination: improved, notes: throughout his hospital stay; Oxygen saturation: within normal limits; Oxygen saturation: 88 %; PCO2: 39; 53; pH body fluid: 7.49; 7.37; PO2: 79; 309; Polymerase chain reaction: Negative; Respiratory rate: 16; Urine analysis: Positive, notes: leukocyte esterase; Positive, notes: moderate amount of bacteria. Therapeutic measures were taken as a result of chronic inflammatory demyelinating polyradiculoneuropathy, condition aggravated, pneumonia aspiration. Additional information: The patient presented to the ED approximately 6 months later with respiratory distress. The patient had received the second Pfizer COVID-19 booster vaccine earlier that same day. His vital signs were temperature of 102 degrees Fahrenheit, heart rate of 154 beats per minute, blood pressure of 105/55, and respiratory rate of 16, oxygen saturation was 88% on non-rebreather mask with 15 Liters of minute of oxygen. ABG showed pH 7.37, pCO2 53 and pO2 309. Notable laboratory values on this admission were aspartate transaminase of 160, alanine aminotransferase of 154, alkaline phosphatase of 353, and a urinalysis that was positive for leukocyte esterase and moderate amount of bacteria. CT scan of the Chest, Abdomen and Pelvis revealed bilateral dependent lung dense consolidations and additional scattered patchy ground glass and consolidative opacities suspicious for aspiration pneumonia and osteomyelitis of the right ischial tuberosity underlying chronic sacral decubitus ulcer. Broad spectrum antibiotics were immediately started and the patient was intubated and mechanically ventilated as the patient had persistent desaturations despite increases in oxygen requirements as well as decreased ventilatory drive. The patient was suspected to have an acute flare of CIDP leading to aspiration pneumonia. The neurology service was consulted and recommended IVIG treatment for 5 days. The patient ultimately underwent a tracheostomy for long term mechanical ventilation. The patient's neurological examination improved throughout his hospital stay, and the patient was discharged to a nursing home with mechanical ventilation and continued plan of monthly IVIG infusions.; Sender's Comments: A possibly contributory role of BNT162B2, BNT162B2 OMI BA.4-5 in triggering the onset of CIDP exacerbation cascades might not be fully excluded, considering the temporal relationship.  More immunological and biomolecular evidence would be needed to explore the plausible physiopathologic mechanism between the vaccination and the event occurrence.  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,Linked Report(s) : US-PFIZER INC-PV202300100633 Same article/drug/patient, different dose/event;