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

Development of an inhibitor was defined as an inhibitor test result of >= 0.60 Bethesda units per milliliter (BU/mL) that was confirmed by a second test result of >=0.60 BU/mL from a separate sample, drawn 2 to 4 weeks after the date when the original sample was drawn, with both tests performed by the central laboratory using Nijmegen-modified Bethesda assay.

ABR was annualized number of bleeding episodes during efficacy period (EP) per participant normalized to a 1-year interval of time. Bleeding episodes were classified as: spontaneous if parent/caregiver/participant records bleeding event when there is no known contributing factor such as definite trauma or antecedent strenuous activity; and traumatic when there is known reason for bleed. ABR=(Number of bleeding episodes during EP/total number of days during EP)*365.25. EP reflects the sum of all intervals of time during which participants were treated with rFIXFc per treatment regimens excluding surgical/rehabilitation periods and large injection intervals (greater than [>]28 days). Participants were included in summary of more than 1 treatment regimen if their regimen changed during study.

Bleeding episodes were classified as spontaneous if parent/caregiver/participant records a bleeding event when there is no known contributing factor such as a definite trauma or antecedent "strenuous" activity. Annualized spontaneous joint bleeding episodes=(Total number of spontaneous joint bleeding episodes during efficacy period (EP) divided by total number of days during EP)*365.25. EP reflects the sum of all intervals of time during which participants were treated with rFIXFc per treatment regimen excluding major and minor surgical/rehabilitation periods and large injection intervals (>28 days). Participants were included in summary of more than 1 treatment regimen if their regimen changed during study.

Using e-diary, each participant's parent/caregiver rated treatment response to any bleeding episode (BE) at approximately 8 to 12 hours from time of injection and prior to additional doses of rFIXFc given for same BE using 4-point scale:- 1=Excellent: abrupt pain relief and/or improvement in signs of bleeding within approximately 8 hours after initial injection; 2=Good: definite pain relief and/or improvement in signs of bleeding within approx. 8 hours after injection, but possibly requiring more than 1 injection after 24-48 hours for complete resolution; 3=Moderate: Probable/slight beneficial effect within 8 hours after initial injection and requires more than 1 injection and 4=None: No improvement or condition worsens within approx. 8 hours after initial injection. Participants were included in summary of more than 1 treatment regimen if their regimen changed during study.

An ED was defined as a 24-hour period in which a participant received one or more doses of rFIXFc injections, with the time of the first injection of rFIXFc defined as the start of the ED. Participant who did not have a particular injection type were counted as having zero injections for that type.

Total annualized rFIXFc consumption (in IU/kg) was calculated for each participant as: Annualized consumption = (Total IU/kg of rFIXFc during efficacy period (EP) divided by total number of days during EP)*365.25. EP reflects the sum of all intervals of time during which participants were treated with rFIXFc according to the treatment regimens of the study excluding surgical/rehabilitation periods and large injection intervals (> 28 days). Participants were included in summary of more than 1 treatment regimen if their regimen changed during study.

Number of injections of rFIXFc required to resolve a bleeding episode during efficacy period (EP) were reported. EP reflects the sum of all intervals of time during which participants were treated with rFIXFc according to the treatment regimens of the study excluding surgical/rehabilitation periods and large injection intervals (>28 days). All injections given from the initial sign of a bleed, until the last date/time within the bleed window were counted. Participants were included in summary of more than 1 treatment regimen if their regimen changed during study.

The average dose of rFIXFc per injection per bleeding episode was calculated as the average of all doses (IU/kg) administered to treat the bleeding episode during efficacy period (EP). EP begins with the first treatment regimen dose of rFIXFc and ends with the last dose (regardless of the reason for dosing). Surgery/rehabilitation periods are not included in the EP. Participants were included in summary of more than 1 treatment regimen if their regimen changed during study.

Blood samples were taken at trough and Cmax (maximum concentration) for assessment of incremental recovery, measured by the one-stage clotting assay. IR (International Units per deciliter [IU/dL] per IU/kg) = (Cmax for FIX activity - Pre-dose FIX activity) (IU/dL)/ Actual dose (IU/kg), where Cmax is 30 minute FIX activity post-dose and FIX activity less than (<)0.5 IU/dL was set to 0 IU/dL for calculation of IR.