Covid and flu vaccine associated transverse myelitis.; left lower extremity weakness; left thigh numbness; she felt lightheaded; left thigh tingling; unable to walk independently; sensation to light touch was diffusely decreased; urine retention; Initial information received on 19-Jun-2023 by health care professional from country regarding an unsolicited valid serious case issued from a literature article.    This case involves a 78 years old female patient who experienced covid and flu vaccine associated transverse myelitis (myelitis transverse) while receiving vaccines PFIZER BIONTECH COVID-19 VACCINE, MODERNA COVID-19 VACCINE and INFLUENZA VACCINE.  The patient with medical history of atrial fibrillation, hypertension, hyperlipidemia, and osteoporosis.  The patient had previously received the Moderna (12/2020, 01/2021) and Pfizer-BioNTech (10/2021, 04/2022) COVID vaccines. She developed symptoms 6 days after receiving the bivalent Pfizer-BioNTech booster and a seasonal influenza vaccine produced by unknown manufacturer lot number not reported via unknown route in unknown administration site in September 2022.  She presented with left lower extremity weakness (muscular weakness) and left thigh numbness (hypoaesthesia). The patient was walking when she felt lightheaded (dizziness) and developed left thigh tingling (paraesthesia) followed by left leg weakness. She presented the next day unable to walk independently (gait inability). On physical exam of the left lower extremity, strength was 4/5 for flexion and extension of the hip and knee, sensation to light touch was diffusely decreased (hyporesponsive to stimuli), and Babinski sign was positive. Laboratory workup including ESR Erythrocyte sedimentation rate), CRP (C-reactive protein), CK (creatine phosphokinase), vitamin B12, and ANA (Antinuclear antibody) were within normal limits. Brain MRI (Magnetic resonance imaging) was unremarkable. Initial spinal MRI showed a nonspecific, nonenhancing lesion with T2 hyperintensity at T5-6. Further serum and CSF (Cerebrospinal fluid) evaluation including anti-MOG (myelin oligodendrocyte glycoprotein) and anti-AQP4 (aquaporin 4) antibodies, ACE (Angiotensin-converting-enzyme) level, and oligoclonal bands was negative. Due to progression of symptoms including urine retention (urinary retention), MRI was repeated on hospital day 10 which demonstrated left parasagittal and posterior cord signal abnormality at T5-T6 with T2-hyperintensity and pathologic contrast enhancement. She denied any recent infectious event or common infectious symptoms. However, she had received COVID and influenza vaccines 6 days prior to symptom onset. She was diagnosed with transverse myelitis (TM) and started on intravenous methylprednisolone 1 gram daily for 5 days with improvement in weakness and sensation.   Of note, initial MRI of her spinal cord lesion was non-enhancing and nonspecific. Given progression of symptoms and lack of an alternative diagnosis, repeat imaging was obtained which demonstrated an enhancing lesion consistent with TM. Parainfectious and postvaccination myelitis often have nonspecific findings on MRI. While TM typically presents with long-segment T2 hyperintensity with enhancement, enhancement is more common in subacute stages than at initial presentation. Within the framework of high value care, repeat imaging should be considered when there is a high index of suspicion for TM.  Action taken: Not applicable  Corrective treatment: methylprednisolone Outcome: Recovering Seriousness criteria: Medically significant  Reporter causality: Related; Sender's Comments: Sanofi company comment dated 22-Jun-2023: This case involves a 78 years old female patient who experienced covid and flu vaccine associated transverse myelitis (myelitis transverse) while receiving vaccine INFLUENZA VACCINE. Based on information received the causal role of VACCINE cannot be excluded due to compatible temporal relationship of ADR to the VACCINE. Further information regarding concurrent condition during vaccination, previous vaccination, tolerance, allergic history excluding alternative etiologies for the reported event are needed to fully assess this case. Based upon the reported information, the role of vaccine cannot be assessed.