Explore the Efficacy and Mechanism of Action of Tezepelumab in Eosinophilic Granulomatosis With Polyangiitis

Inclusion Criteria: 1. Capable of providing written informed consent 2. Eosinophilic granulomatosis with polyangiitis is defined as a history of asthma, a blood eosinophil level of 10% or an absolute eosinophil count of more than 1.0 x10\^9/L, and the presence of two or more criteria: \- Histopathological evidence of eosinophilic vasculitis \- Perivascular eosinophilic infiltration, or eosinophil-rich granulomatous inflammation \- Neuropathy \- Pulmonary infiltrate * Sino-nasal abnormality * Cardiomyopathy * Glomerulonephritis * Alveolar haemorrhage * Palpable purpura * Anti-neutrophil cytoplasmic antibody \[ANCA\] positivity 3. History of one or more flares of EGPA in 24 months prior to screening. EGPA flares will be defined as worsening or persistence of active disease characterised by: \- Active vasculitis (BVAS \>0); OR \- An asthma exacerbation/asthma worsening OR \- Active nasal and/or sinus disease Warranting: \- Rescue use of prednisolone for 3 or more days OR an increase in background prednisolone dose by at least 5 mg daily for at least three days OR \- An increased dose or addition of immunosuppressive therapy; OR * Hospitalisation related to EGPA worsening 4. Blood eosinophil level at screening (visit 1) of ≥ 0.2 x10\^9/L (participants can be re screened once within 2 weeks if the BEC is \< 0.2 x10\^9/L at the initial screening assessment). n.b. This criterion is not relevant for participants taking background anti-IL-5/5R biological agents mepolizumab (MEPO) or benralizumab (BRZ) in which any baseline blood eosinophil count (BEC) permitted. 5. Non severe EGPA according to the American College of Rheumatology 2021 definition. Non-Severe EGPA: Vasculitis without life- or organ-threatening manifestations (e.g., rhinosinusitis, asthma, mild systemic symptoms, uncomplicated cutaneous disease, mild inflammatory arthritis). 6\. Stable dose of prednisolone (≥5.0 to ≤30.0 mg per day, with or without additional Immunomodulatory therapy) for at least 4 weeks before the baseline visit. 7\. Immunomodulatory therapy: (i) If receiving non-biologic immunomodulatory therapy, the dosage must be stable for the 4 weeks prior to baseline visit. (ii) Patients on background anti-IL-5/5R therapy (either MEPO or BRZ) at any licensed dose for the current clinical indications of severe asthma and EGPA in the UK and Europe respectively AND have been on treatment for at least 6 months. n.b. participants on background anti-IL-5/5R therapy will be capped to no more than 50% of the total sample size. Exclusion Criteria: 1. Diagnosis of Granulomatosis with polyangiitis (GPA) or microscopic polyangiitis (MPA). 2. Pregnancy or unable to use a highly effective method of birth control (confirmed by the Investigator) from randomisation throughout the study duration and within 8 weeks after last dose of IMP. 3. Active life- or organ-threatening manifestations of EGPA within 6 months prior to screening, defined as: * Severe alveolar haemorrhage * Rapidly progressive glomerulonephritis * Severe gastrointestinal or central nervous system involvement requiring intensification of immunosuppression or surgery * Severe cardiac involvement including life threatening arrhythmia, heart failure with an ejection fraction \< 20% or acute myocardial infarction or active myocarditis 4. Current active malignancy. 5. Immunodeficiency including HIV 6. Helminth infection within 6-months of screening that has not been treated or remains refractory to treatment. 7. Unstable liver disease with the exception of Gilberts syndrome or asymptomatic gallstones. 8. Use of a prohibited concurrent medication as listed below: * Biologic therapy for severe asthma (except MEPO or BRZ) within 4 months or 5 half-lives (whichever is longer) prior to Visit 1 or receipt of any investigational non-biologic agent within 30 days or 5 half-lives (whichever is longest) prior to Visit 1. * Biologic therapies for EGPA including Rituximab and Alemtuzumab within 6 months of visit 1. * IV or SC immunoglobulin therapy within 3 months of visit 1. * Oral cyclophosphamide within 6 weeks of screening or IV cyclophosphamide within 4 months of visit 1. * IM or IV corticosteroids within 6 weeks of visit 1. 9. Known adrenal insufficiency (primary or secondary), that in the opinion of the investigator and clinical care team preclude maintenance oral steroid tapering