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

Key Inclusion Criteria:

- Weight >=3.5 kilogram at the time of informed consent

- Severe hemophilia B defined as <=2 IU/dl (<=2%) endogenous factor IX 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 is defined based
on a patient'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 Recombinant Coagulation
Factor IX Fc Fusion Protein (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 make the subject unsuitable for enrollment (example HIV infection
with 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 is allowed. Treatment in these circumstances
should not exceed 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, make
the subject unsuitable for enrollment

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