Phase 3, Open-label, Single-dose, Multicenter Study Investigating Efficacy, Safety, and Tolerability of CSL222 (Etranacogene Dezaparvovec) Administered to Adolescent Male Subjects (≥ 12 to < 18 Years of Age) With Severe or Moderately Severe Hemophilia B

Inclusion Criteria: * Key Inclusion Criteria for the Lead-in Period: Assigned male sex at birth * Aged ≥138 months (11 years and 6 months) to less than (\<) 206 months (17 years and 2 months) at the time of informed consent / assent. * Congenital hemophilia B with known severe or moderately severe FIX deficiency (less than or equal to \[≤\] 2% of normal circulating FIX) for which the participant has been on continuous FIX prophylaxis. * On stable continuous FIX prophylaxis for at least 2 months before Screening. * Minimum of 75 previous exposure days of treatment with FIX protein before Scr…