RecruitingPhase 3Genetic interventionPhase 3, Open-label, Single-dose Study of CSL222 in Adolescent Male Subjects (≥ 12 to < 18 Years of Age) With Severe or Moderately Severe Hemophilia BThis is a phase 3, prospective, open-label, single-arm, single-dose, multicenter study investigating the efficacy, safety, and tolerability of CSL222 (AAV5-hFIXco-Padua) in adolescent male participants with severe or moderately severe hemophilia B.