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

Main inclusion criteria: * Age 18-80 years. * Documented physician diagnosed asthma requiring continuous treatment with high-dose ICS plus a 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. * Documented long-term OCS therapy for asthma, equivalent to a daily dose of at least 5 mg and up to 40 mg of prednisone/prednisolone for at least 3 continuous months directly preceding Visit 1. * Participant should be on a stable maintenance OCS dose for at least 4 weeks prior to Visit 1. * Documented history of at least 1 asthma exacerbation event within 12 months prior to Visit 1. Other inclusion criteria per protocol apply. Main exclusion criteria: * Pulmonary disease or systemic diseases, other than asthma associated with elevated peripheral EOS counts. * Any disorder or major physical impairment that is not stable and could affect the safety of the participant throughout the study, influence the findings of the study or the interpretation, or impede the participant's ability to complete the entire duration of study. * History of cancer. * History of a clinically significant infection requiring treatment with antibiotics, antiviral or additional corticosteroid medications finalised \< 2 weeks before Visit 1. * A helminth parasitic infection diagnosed within 6 months prior to Visit 1 that has not been treated with, or has failed to respond to, standard of care therapy. * Current smokers or participants with smoking history ≥ 10 pack-years and participants using vaping products, including electronic cigarettes. * History of chronic alcohol or drug abuse within 12 months prior to Visit 1. * Tuberculosis requiring treatment within the 12 months prior to Visit 1. * History of known immunodeficiency disorder including a positive HIV test at Visit 1. * Major surgery within 8 weeks prior to Visit 1 or planned surgical procedures requiring general anaesthesia or inpatient status for \> 1 day during the conduct of the study. * Coexistent inflammatory conditions for which long-term OCS doses are part of their maintenance treatment. * Receipt of any marketed or investigational biologic agent within 4 months or 5 half-lives (whichever is longer) prior to Visit 1 or receipt of any investigational nonbiologic agent within 30 days or 5 half-lives (whichever is longest) prior to Visit 1. Participants enrolled in current or previous tezepelumab studies will not be included. * Concurrent enrolment in another clinical study involving an IP. * Treatment with systemic immunosuppressive/immunomodulating drugs, except for OCS used in the treatment of asthma/asthma exacerbations, within the last 12 weeks or 5 half-lives (whichever is longer) prior to Visit 1. * History of anaphylaxis or documented immune complex disease (Type III hypersensitivity reactions) following any biologic therapy. * Positive hepatitis B surface antigen, or hepatitis C virus antibody serology at screening, or a positive medical history for hepatitis B or C. * Pregnant, breastfeeding, or lactating women. Other exclusion criteria per protocol apply.