Study of IFX-1 to Replace Steroids in Patients With Granulomatosis With Polyangiitis and Microscopic Polyangiitis.

Inclusion Criteria: * Diagnosis of granulomatosis with polyangiitis (GPA) or microscopic polyangiitis (MPA) * Have ≥ 1 "major" item, or ≥ 3 other items, or ≥ 2 renal items on the Birmingham Vasculitis Activity Score Version 3 (BVASv3). * Newly diagnosed or relapsed GPA or MPA that requires treatment with Cyclophosphamide (CYC) or Rituximab (RTX) plus GCs. * Glomerular filtration rate ≥ 20 mL/min/1.73 m². Exclusion Criteria: * Any other multi-system autoimmune disease. * Require mechanical ventilation at screening. * Known hypersensitivity to any investigational medicinal product and/or any excipient. * Rare hereditary problems of galactose intolerance, total lactase deficiency or glucose-galactose malabsorption. * Have required management of infections, as follows (a) Chronic infection requiring anti-infective therapy within 3 months before screening. (b) Use of intravenous antibacterials, antivirals, anti-fungals, or anti-parasitic agents within 30 days of screening * Current and/or history (within the previous 5 years) of drug and/or alcohol abuse and/or dependence. * Evidence of Hep B, C and/ or HIV infection. Only subjects with documented negative historical results (within 4 weeks before screening) for Hep B,C Virus and HIV or a negative test by Screening can be included into the study. * Abnormal laboratory findings at screening * Current or history of malignancy, lymphoproliferative, or myeloproliferative disorder * Received CYC or RTX within 12 weeks before screening or within 12 weeks before CYC or RTX is started for remission induction within 2 weeks before screening. * Received \> 3 g cumulative intravenous GCs within 4 weeks before screening. * Received an oral daily dose of a GC of \> 10 mg prednisone-equivalent for more than 6 weeks continuously prior to screening. * Received an oral daily dose of a GC of \> 80 mg prednisone equivalent within 2 weeks before screening. * Received a CD20 inhibitor, anti-tumor necrosis factor treatment, abatacept, alemtuzumab, any other experimental or biological therapy, intravenous immunoglobulin (Ig) or plasma exchange, antithymocyte globulin, or required renal dialysis within 12 weeks before screening. * Received a live vaccination within 4 weeks before screening * Either active or latent tuberculosis treatment is ongoing. * Pregnant or lactating. * Abnormal electrocardiogram. * Female subjects of childbearing potential unwilling or unable to use a highly effective method of contraception * Participation in an investigational clinical study during the 12 weeks before screening. * Male subjects with female partners of childbearing potential unwilling to use contraception