Study to Determine the Safety and Efficacy of rFIXFc in Previously Untreated Males With Severe Hemophilia B

An Open-Label, Multicenter Evaluation of the Safety and Efficacy of Recombinant Coagulation Factor IX Fc Fusion Protein (rFIXFc; BIIB029) in the Prevention and Treatment of Bleeding in Previously Untreated Patients With Severe Hemophilia B

The primary objective of the study was to evaluate the safety of recombinant coagulation factor IX Fc fusion protein (rFIXFc, BIIB029) in previously untreated patients (PUPs) with severe hemophilia B. Secondary objectives were to evaluate the efficacy of rFIXFc in the prevention and treatment of bleeding episodes in PUPs, and to evaluate rFIXFc consumption for prevention and treatment of bleeding episodes in PUPs.

Key Inclusion Criteria:

• Weight >=3.5 kilogram at the time of informed consent.
• Severe hemophilia B was defined as less than or equal to (<=)2 International Units per deciliter (IU/dL) (<=2 percent [%]) endogenous FIX documented in the medical record or as tested during the Screening Period.

Key Exclusion Criteria:

• History of positive inhibitor testing. A prior history of inhibitors was defined based on a participant's historical positive inhibitor test using the local laboratory Bethesda value for a positive inhibitor test (that is equal to or above lower limit of detection).
• History of hypersensitivity reactions associated with any rFIXFc administration.
• Exposure to blood components or injection with a coagulation factor IX (FIX) concentrate (including plasma derived) other than rFIXFc.
• Injection with commercially available rFIXFc more than 28 days prior to Screening.
• More than 3 injections of commercially available rFIXFc prior to confirmation of eligibility.
• Other coagulation disorders in addition to hemophilia B.
• Any concurrent clinically significant major disease that, in the opinion of the Investigator, would have made the participant unsuitable for enrollment (example HIV infection with cluster of differentiation 4 (CD4) lymphocyte count less than (<)200 cells/microliter (mcL) or a viral load greater than (>)200 particles/mcL, or any other known congenital or acquired immunodeficiency).
• Current systemic treatment with chemotherapy and/or other immunosuppressant drugs. Use of steroids for treatment of asthma or management of acute allergic episodes or otherwise life-threatening episodes was allowed. Treatment in these circumstances should not have exceeded a 14-day duration.
• Participation within the past 30 days in any other clinical study involving investigational treatment.
• Current enrollment in any other clinical study involving investigational treatment.
• Inability to comply with study requirements.
• Other unspecified reasons that, in the opinion of the Investigator or Bioverativ, would have made the participant unsuitable for enrollment.

NOTE: Other protocol-defined inclusion/exclusion criteria may apply.