Adverse events (AEs) include any untoward medical occurrence in a trial participant administered a study drug and does not necessarily have a causal relationship with this treatment. AEs include worsening of a pre-existing medical condition and laboratory value changes requiring therapy or adjustment in prior therapy. AEs were assessed for severity according to the Common Terminology Criteria for Adverse Events (CTCAE), Version 3, where Grade 1 = Mild AE, Grade 2 = Moderate AE, Grade 3 = severe AE, Grade 4 = life-threatening AE and Grade 5 = death due to AE. Relationship to study treatment was determined by the investigator. A serious adverse event (SAE) is defined as an AE that met 1 or more of below criteria: * was fatal; * was life threatening; * required in-patient hospitalization or prolongation of existing hospitalization; * resulted in persistent or significant disability/incapacity; * was a congenital anomaly/birth defect; * other significant medical hazard.

All study samples (tezepelumab and placebo) were tested using an electrochemiluminescence (ECL) based immunoassay to detect and confirm the presence of antibodies capable of binding to tezepelumab. Samples identified as positive in the immunoassay were tested in a receptor-binding ECL-based assay to detect neutralizing or inhibitory effects toward tezepelumab. The number of participants with positive anti-tezepelumab binding antibodies / neutralizing antibodies at any time post-baseline with a negative or no result at baseline is reported.