A Phase 3, Open-label, Uncontrolled Single-arm Study to Evaluate the Efficacy, Pharmacokinetics, and Safety of Avacopan in Combination With a Rituximab or a Cyclophosphamide-containing Regimen in Children From 6 Years to < 18 Years of Age With Active ANCA-associated Vasculitis (AAV)

Inclusion Criteria: * Male and female children and adolescents from 6 to \< 18 years old of age. * Clinical diagnosis of Granulomatosis with Polyangiitis (GPA) or microscopic polyangiitis (MPA), consistent with Chapel-Hill Consensus Conference definitions (Jennette et al, 2013). * Positive anti-PR3(Anti-Proteinase 3) or anti-MPO(Anti-Myeloperoxidase) antibody documented at Screening or historically. Historical positivity is acceptable (even if Screening is negative) if supported by verifiable lab source documentation obtained during AAV diagnosis or disease course; use the most recent positiv…