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

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.