A Trial to Investigate Benralizumab in Children With Eosinophilic Diseases

Prior treatment

• Previous receipt of benralizumab in an interventional clinical study.
  • EGPA Cohort:
• Diagnosed with granulomatosis with polyangiitis (previously known as Wegener'granulomatosis) or microscopic polyangiitis.
• EGPA relapse: any deterioration in EGPA and/or organ-threatening EGPA that per Investigator judgement renders participants unstable in their EGPA within 3 months prior to screening (Visit 1) and through first administration of IP at baseline (Visit 2).
• Life-threatening EGPA: imminently life-threatening EGPA disease within 3 months prior to screening (Visit 1) and through first administration of IP at baseline (Visit 2), as per Investigator judgement.
  • HES Cohort:

Other illness

• Any current malignancy or history of malignancy.
• History of anaphylaxis to any biologic therapy or vaccine.
• Known, pre-existing, clinically significant endocrine, autoimmune, metabolic, neurological, renal, gastrointestinal, hepatic, haematological, respiratory, or any other system abnormalities.

Other

• All Cohorts:
• Life-threatening HES or HES complications, as judged by the investigator.
• Hypereosinophilia of unknown significance (HE-US).
• Diagnosis of systemic mastocytosis.

• All Cohorts:
• Male or female participants must be aged 6 to \< 18 years of age at the time of signing the assent form and their caregiver signing the informed consent form.
• Body weight greater than (\>=) 15 kilograms (kg).
  • EGPA Cohort:
• Therapy with corticosteroids: The prescribed dose of oral corticosteroids (OCS) (greater than \[\>\] 0.1 milligrams per kilogram per day (mg/kg/day), max dose of 50 milligrams per day (mg/day) must be stable (that is, no adjustment of the dose) for at least 4 weeks prior to baseline (Visit 2).
• Immunosuppressive therapy: If receiving immunosuppressive therapy, the dosage must be stable for at least 4 weeks prior to baseline (Visit 2).
  • HES Cohort:
• Documented HES diagnosis, defined as history of persistent eosinophilia \>1500 cells/µL without secondary cause on 2 examinations ≥1 month apart and evidence of eosinophil-mediated organ involvement.
• Symptomatic active HES, or history of a prior flare, or considered eligible based on disease severity per investigator judgement.
• AEC ≥1000 cells/µL at screening (Visit 1).
• Documented negative testing for Fip1-like 1 gene fused with the platelet-derived growth factor receptor alpha gene (FIP1L1-PDGFR) fusion tyrosine kinase gene translocation.