Study to Evaluate Efficacy and Safety of Benralizumab in Reducing Oral Corticosteroid Use in Adult Patients With Severe Asthma

Inclusion Criteria: 1. Peripheral blood eosinophil count of ≥150 cells/μL assessed by central lab at Visit 1 or ≥ 300 cells/μL in the past 12 months 2. History of physician diagnosed asthma requiring continuous treatment with high dose ICS (high-dose ICS is budesonide/formoterol HFA ≥640/18 per day or equivalent, fluticasone propionate DPI \> 500/day or equivalent, or authorized generics for these products) plus LABA for at least 6 months prior to Visit 1. The ICS and LABA can be contained within a combination product or given by separate inhalers. The ICS can also be given via nebulized solution for inhalation. 3. Chronic oral corticosteroid therapy equivalent to a daily dose of at least 5 mg of prednisone, for at least 3 continuous months directly preceding Visit 1. 4. Patient should be on a stable OCS dose for at least 4 weeks prior to Visit 1. 5. Non-smokers, current smokers or former smokers with a smoking history of \< or =20 pack-years at Visit 1 Exclusion Criteria: 1. Clinically important pulmonary disease other than asthma or ever been diagnosed with pulmonary or systemic disease, other than asthma, that are associated with elevated peripheral eosinophil counts 2. Known history of allergy or reaction to the study drug formulation 3. History of anaphylaxis to any biologic therapy 4. A helminth parasitic infection diagnosed within 24 weeks prior to the date informed consent is obtained that has not been treated with, or has failed to respond to, standard of care therapy 5. Asthma exacerbation requiring use of systemic corticosteroids, or an increase in maintenance dose of OCS, or acute upper/lower respiratory infections requiring antibiotics or antiviral medication within 30 days prior to Visit 2 (first benralizumab dose) 6. A history of known immunodeficiency disorder including history of a positive human immunodeficiency virus (HIV) test 7. Alanine aminotransferase (ALT) or aspartate aminotransferase (AST) level ≥3 times the upper limit of normal (ULN) confirmed at Visit 1. 8. Receipt of immunoglobulin or blood products within 30 days prior to the date informed consent is obtained 9. Coincident primary adrenal failure (Addison's disease) or irreversible secondary hypoadrenalism due to another independent cause (e.g. pituitary tumour or its treatment) 10. Co-existent inflammatory conditions for which chronic OCS doses are part of their maintenance treatment such as Giant Cell Arteritis, Polymyalgia Rheumatica 11. Exclusion from genetic research may be for any of the exclusion criteria specified in the main study or allogeneic bone marrow transplant, Non-leukocyte depleted whole blood transfusion within 120 days of genetic sample collection 12. Current night-shift workers