Study to Evaluate Avacopan in Combination With a Rituximab or Cyclophosphamide-containing Regimen, in Children From 6 Years to < 18 Years of Age With AAV.

Change From Baseline Over 52 Weeks in Urinary Albumin-Creatinine Ratio (UACR)

Time frame: Baseline up to Week 52

Change From Baseline Over 52 Weeks in Estimated Glomerular Filtration Rate (eGFR)

Time frame: Baseline up to Week 52

Change From Baseline Over 52 Weeks In Physician Global Assessment (PGA) of Disease Activity

Time frame: Baseline up to Week 52

Change From Baseline Over 52 Weeks in Pediatric Vasculitis Damage Index (PVDI)

Time frame: Baseline up to Week 52

Number of Glucocorticoid Dosages Administered

Time frame: Screening up to Week 52

Proportion of Participants Across the Taste Score Categories of the TASTY Faces Scale

The TASTY faces scale will be utilized to assess the taste of the oral pediatric formulation. A 7-point version of the scale will be used, where higher scores correspond to faces showing favorable tastes. Upon drug administration, the child will be shown the TASTY scale and asked to rate his/her perception of tastiness by pointing to the appropriate face on the scale.

Time frame: Day 1 and Week 2

Taste and Acceptability Score of Avacopan per TASTY Faces Scale

The TASTY faces scale will be utilized to assess the taste of the oral pediatric formulation. A 7-point version of the scale will be used, where higher scores correspond to faces showing favorable tastes. Upon drug administration, the child will be shown the TASTY scale and asked to rate his/her perception of tastiness by pointing to the appropriate face on the scale.

Time frame: Day 1 and Week 2