Inhibitor development was defined as an inhibitor result of greater than or equal to (>=0.6) Bethesda units (BU/mL) that was confirmed by a second test result from a separate sample, drawn 2 to 4 weeks following the date when the original sample was drawn. Both tests must have been performed by the central laboratory using the Nijmegen modified Bethesda assay.

Analysis was performed on safety analysis set which included all participants who took at least 1 dose of study intervention.

ABR: annualized number of treated bleeding episodes (BE) per participant per year. ABR=number of treated BE during efficacy period (EP)/total number of days during EP*365.25. Treated BE:any occurrence of hemorrhage required administration of BIVV001. It started from 1st sign of bleed and ended no more than 72 hours after last injection to treat BE, any subsequent bleeding at same location/injections administered less than or equal to (<=) 72 hours apart from previous injection were considered same BE. Any injection after >72 hours post preceding one=considered 1st injection to treat new BE in same location. Any bleed at different location:considered as separate BE, regardless of time from last injection. EP=sum of all intervals of time during which participants were treated with BIVV001 according to study arms and treatment regimens. ABR:by negative binomial model with total number of treated BE during EP as response variable and log transformed EP duration (years) as offset variable.

Analysis was performed on FAS population.

ABR: annualized number of treated BE per participant per year. ABR = number of treated BE during EP/total number of days during EP*365.25. Treated BE: any occurrence of hemorrhage that required administration of BIVV001. It started from 1st sign of bleed and ended no more than 72 hours after last injection to treat BE, any subsequent bleeding at same location/injections administered <=72 hours apart from previous injection were considered same BE. Any injection to treat bleed, taken >72 hours after preceding one, was considered 1st injection to treat new bleeding episode in same location. Any bleed at different location: considered as separate BE, regardless of time from last injection. EP reflects sum of all intervals of time during which participants were treated with BIVV001 according to study arms and treatment regimens. ABR: using negative binomial (NB) model with total number of treated BE during EP as response variable and log-transformed EP duration (years) as offset variable.

Analysis was performed on FAS population. Sensitivity analysis excluded 1 participant who did not receive weekly prophylaxis treatment as specified in the protocol for an extended period of time.

ABR:annualized number of all BE (treated and untreated)/participant/year. ABR=number of all BE during EP/total number of days during EP*365.25. BE:any occurrence of hemorrhage required administration of BIVV001. It started from 1st sign of bleed and ended no more than 72 hours after last injection to treat BE, any subsequent bleeding at same location/injections administered <=72 hours apart from previous injection were considered same BE. Any injection after >72 hours post preceding one=considered 1st injection to treat new BE in same location. Any bleed at different location: considered as separate BE, regardless of time from last injection. EP:sum of all intervals of time during which participants treated with BIVV001 according to study arms & treatment regimens. ABR:NB model with total number of treated BE during EP as response variable and log-transformed EP duration (years) as offset variable. Spontaneous:bleeding without contributing factor, Traumatic:bleeding with known reason.

Analysis was performed on FAS population.

ABR: annualized number of all BE (treated & untreated)/participant/year. ABR=number of all BE during EP/total number of days during EP*365.25. BE: any hemorrhage occurrence required administration of BIVV001. It started from 1st sign of bleed & ended no more than 72 hours after last injection to treat BE, any subsequent bleeding at same location/injections administered <=72 hours apart from previous injection were considered same BE. Any bleed at different location: considered as separate BE, regardless of time from last injection. EP: sum of all intervals of time during which participants treated with BIVV001 according to study arms and treatment regimens. ABR: estimated by NB model with total number of treated BE during EP as response variable and log-transformed EP duration (years) as offset variable. Spontaneous: bleeding without contributing factor (definite trauma/antecedent strenuous activity). Traumatic: bleeding with known/believed reason.

Analysis was performed on FAS population. Sensitivity analysis excluded 1 participant who did not receive weekly prophylaxis treatment as specified in the protocol for an extended period of time.

ABR: annualized number of treated bleeding episodes per participant per year. ABR = number of all BE during EP/total number of days during EP*365.25. EP reflects sum of all intervals of time during which participants were treated with BIVV001 according to study arms and treatment regimens. Treated BE: episode that started from 1st sign of bleed and ended no more than 72 hours after last injection to treat bleeding episode, any subsequent bleeding at same location/injections administered <=72 hours apart from previous injection were considered same bleeding episode. Any injection to treat bleed, taken >72 hours after preceding one was considered 1st injection to treat new BE in same location. Any bleed at different location was considered as separate bleeding episode, regardless of time from last injection. Spontaneous bleeding: BE without contributing factor (definite trauma/antecedent "strenuous" activity). Traumatic bleeding: BE with known/believed reason for bleed.

Analysis was performed on FAS population.

ABR: annualized number of treated bleeding episodes per participant per year. ABR = number of all BE during EP/total number of days during EP*365.25. EP reflects sum of all intervals of time during which participants were treated with BIVV001 according to study arms and treatment regimens. Treated BE: episode that started from 1st sign of bleed and ended no more than 72 hours after last injection to treat bleeding episode, any subsequent bleeding at same location/injections administered <=72 hours apart from previous injection were considered same bleeding episode. Any injection to treat bleed, taken >72 hours after preceding one, was considered 1st injection to treat new BE in same location. Any bleed at different location was considered as separate bleeding episode, regardless of time from last injection. Spontaneous bleeding: BE without contributing factor (definite trauma/antecedent "strenuous" activity). Traumatic bleeding: BE with known/believed reason for bleed.

Analysis was performed on FAS population. Sensitivity analysis excluded 1 participant who did not receive weekly prophylaxis treatment as specified in the protocol for an extended period of time.

ABR: annualized number of treated bleeding episodes per participant per year. ABR = number of all BE during EP/total number of days during EP*365.25. Efficacy period reflects sum of all intervals of time during which participants were treated with BIVV001 according to study arms and treatment regimens. Treated bleeding episode: episode that started from 1st sign of bleed and ended no more than 72 hours after last injection to treat bleeding episode, any subsequent bleeding at same location/injections administered <=72 hours apart from previous injection were considered same bleeding episode. Any injection >72 hours after preceding one, was considered 1st injection to treat new BE in same location. Any bleed at different location was considered as separate bleeding episode, regardless of time from last injection. Spontaneous bleeding: BE without contributing factor (definite trauma/antecedent "strenuous" activity). Traumatic bleeding: BE with known/believed reason for bleed.

Analysis was performed on FAS population.

ABR: annualized number of treated bleeding episodes per participant per year. ABR = number of all BE during EP/total number of days during EP*365.25. EP reflects sum of all intervals of time during which participants were treated with BIVV001 according to study arms & treatment regimens. Treated BE: episode that started from 1st sign of bleed and ended no more than 72 hours after last injection to treat bleeding episode any subsequent bleeding at same location/injections administered <=72 hours apart from previous injection were considered same bleeding episode. Any injection to treat bleed, taken >72 hours after preceding one, was considered 1st injection to treat new BE in same location. Any bleed at different location was considered as separate bleeding episode, regardless of time from last injection. Spontaneous bleeding: BE without contributing factor (definite trauma/antecedent "strenuous" activity). Traumatic bleeding: BE with known/believed reason for bleed.

Analysis was performed on FAS population. Sensitivity analysis excluded 1 participant who did not receive weekly prophylaxis treatment as specified in the protocol for an extended period of time.

FVIII activity level was measured using activated partial thromboplastin time (aPTT)-based one stage clotting assay. Percentage of participants who achieved steady-state trough FVIII activity levels above (>) 1%, 3%, 5%, 10%, 15%, and 20% were reported in this outcome measure. Participants were counted in more than one category, as applicable.

Analysis was performed on FAS. Here, 'overall number of participants analyzed = participants with available data for this outcome measure.

A bleeding episode was defined as an episode that started from 1st sign of bleed and ended no more than 72 hours after last injection to treat bleeding episode, any subsequent bleeding at same location or injections administered <=72 hours apart from previous injection were considered same bleeding episode. Any injection to treat bleed, taken >72 hours after preceding one, was considered 1st injection to treat new BE in same location. Any bleed at different location was considered as separate bleeding episode, regardless of time from last injection.

Analysis was performed on FAS. Here, 'overall number of units analyzed' = total number of treated bleeding episodes.

A bleeding episode was defined as an episode that started from 1st sign of bleed and ended no more than 72 hours after last injection to treat bleeding episode, any subsequent bleeding at same location or injections administered <=72 hours apart from previous injection were considered same bleeding episode. Any injection to treat bleed, taken >72 hours after preceding one, was considered 1st injection to treat new BE in same location. Any bleed at different location: considered as separate BE, regardless of time from last injection.

Analysis was performed on FAS excluding 1 participant who did not receive weekly prophylaxis treatment as specified in the protocol for an extended period of time. Here, 'overall number of units analyzed' = total number of treated bleeding episodes.

A bleeding episode was defined as an episode that started from 1st sign of bleed and ended no more than 72 hours after last injection to treat bleeding episode, any subsequent bleeding at same location or injections administered <=72 hours apart from previous injection were considered same bleeding episode. Any injection to treat bleed, taken >72 hours after preceding one, was considered 1st injection to treat new BE in same location. Any bleed at different location: considered as separate BE, regardless of time from last injection. Percentage of bleeding episodes (of all bleeding episodes occurred) which were treated with single injection was reported in this outcome measure.

Analysis was performed on FAS population. Here, 'overall number of units analyzed' = total number of treated bleeding episodes.

A bleeding episode was defined as an episode that started from 1st sign of bleed and ended no more than 72 hours after last injection to treat bleeding episode, any subsequent bleeding at same location or injections administered <=72 hours apart from previous injection were considered same bleeding episode. Any injection to treat bleed, taken >72 hours after preceding one, was considered 1st injection to treat new BE in same location. Any bleed at different location: considered as separate BE, regardless of time from last injection. Percentage of bleeding episodes (of all bleeding episodes occurred) which were treated with single injection was reported in this outcome measure.

Analysis was performed on FAS, excluding the participant who did not receive the weekly prophylaxis treatment as per protocol for an extended period of time. Here, 'overall number of units analyzed' = total number of treated bleeding episodes.

A bleeding episode was defined as an episode that started from 1st sign of bleed and ended no more than 72 hours after last injection to treat bleeding episode, any subsequent bleeding at same location or injections administered <=72 hours apart from previous injection were considered same bleeding episode. Any injection to treat bleed, taken >72 hours after preceding one, was considered 1st injection to treat new BE in same location. Any bleed at different location: considered as separate BE, regardless of time from last injection. Total dose was expressed in unit: International units per kilogram (IU/kg).

Analysis was performed on FAS. Here, 'overall number of units analyzed' = total number of treated bleeding episodes.

A bleeding episode was defined as an episode that started from 1st sign of bleed and ended no more than 72 hours after last injection to treat bleeding episode, any subsequent bleeding at same location or injections administered <=72 hours apart from previous injection were considered same bleeding episode. Any injection to treat bleed, taken >72 hours after preceding one, was considered 1st injection to treat new BE in same location. Any injection after >72 hours post preceding one, was considered 1st injection to treat new BE in same location. Any bleed at different location: considered as separate BE, regardless of time from last injection. Total dose was expressed in unit: IU/kg.

Analysis was performed on FAS, excluding 1 participant who did not receive weekly prophylaxis treatment for an extended period of time. Here, 'overall number of units analyzed' = total number of treated bleeding episodes.

Physicians assessed participant's response to BIVV001 treatment using 4-point response scale categorized as: Excellent= BE responded to fewer than/usual number of injections/less than/usual dose of FVIII/rate of breakthrough bleeding during prophylaxis was <= that usually observed; Effective = most BE responded to same number of injections and dose, but some required more injections/higher doses/there was minor increase in rate of breakthrough bleeding; partially effective = BE most often required more injections and/or higher doses than expected/adequate breakthrough bleeding prevention during prophylaxis required more frequent injections and/or higher doses; Ineffective = routine failure to control hemostasis or hemostatic control required additional agents.

Analysis was performed on FAS. Here, 'overall number of participants analyzed' = participants with available data for this outcome measure.

Participant's response to the 1st injection of BIVV001 treatment for treating a bleed was evaluated by ISTH 4-point response scale categorized as: Excellent (complete pain relief/complete resolution of signs of bleeding), Good (significant pain relief /improvement in signs of bleeding), Moderate (modest pain relief/improvement in signs of bleeding) and none (no or minimal improvement/condition worsened). Assessed approximately 72 hours after initial treatment for BE. Bleeding episode: an episode that started from 1st sign of bleed and ended no more than 72 hours after last treatment for bleed, within which any symptoms of bleeding at same location/injections <=72 hours apart were considered same BE. Any injection after >72 hours post preceding one=considered 1st injection to treat new BE in same location. Any bleed at different location: considered as separate BE, regardless of time from last injection. Participants were counted in more than one category, as applicable.

Analysis was performed on FAS population. Here, 'overall number of units analyzed' = number of injections with a response.

Total annualized BIVV001 consumption (in IU/kg) was calculated for each participant as: Total IU/kg of BIVV001 during 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 BIVV001 according to the study arms and treatment regimens.

Analysis was performed on FAS population.

AJBR: annualized number of joint bleeding/participant/year. ABR = number of treated joint BE during EP divided by total number of days during EP*365.25. Joint BE: unusual sensation in joint ('aura') along with 1) increasing swelling/warmth over skin, joint; 2) increasing pain or 3) progressive loss of range of motion/difficulty in using limb compared to Baseline. BE: episode started from 1st sign of bleed & ended no more than 72 hours after last treatment for bleed, within which any symptoms of bleeding at same location/injections <=72 hours apart considered same BE. Any injection after >72 hours post preceding one=1st injection to treat new BE in same location. Any bleed at different location=separate BE, regardless of time from last injection. EP: sum of all intervals of time during which participants treated with BIVV001 per study arms and treatment regimens. ABR:NB model with total number of treated BE during EP (response variable) & log-transformed EP duration (offset variable).

Analysis was performed on FAS population.

AJBR: annualized number of joint bleeding/participant/year. ABR = number of treated joint BE during EP divided by total number of days during EP*365.25. Joint BE: unusual sensation in joint ('aura') along with 1) increasing swelling/warmth over skin, joint; 2) increasing pain or 3) progressive loss of range of motion/difficulty in using limb compared to Baseline. BE: episode started from 1st sign of bleed & ended no more than 72 hours after last treatment for bleed, within which any symptoms of bleeding at same location/injections <=72 hours apart considered same BE. Any injection after >72 hours post preceding one=1st injection to treat new BE in same location. Any bleed at different location=separate BE, regardless of time from last injection. EP: sum of all intervals of time during which participants treated with BIVV001 per study arms and treatment regimens. ABR: NB model with total number of treated BE during EP (response variable) & log-transformed EP duration (offset variable).

Analysis was performed on FAS population. Sensitivity analysis excluded 1 participant who did not receive weekly prophylaxis treatment as specified in the protocol for an extended period of time.

HJHS is a validated 11-item scoring tool developed for the assessment of joint health in participants with hemophilia. Following domains were assessed for elbows, knee and ankle joints: swelling (score 0 = no swelling to 3=severe), duration of swelling (score 0 = no swelling and 1 = >=6 months), muscle atrophy (score 0 = none to 2 = severe), crepitus on motion (score 0 = none to 2=severe), flexion loss (score 0 = <5' to 3 = >20'), extension loss (score 0 = <5' to 3 = >20'), joint pain (score 0 = no pain through active range of motion to 2 = pain through active range) and strength (score 0 = holds test position with maximum resistance to 4 = trace/no muscle contraction), for each item 0 = no damage and higher score = severe damage.

Analysis was performed on FAS population. Here, 'number analyzed' = participants with available data for each specified category.

Haemo-QoL kids short version: used to measure physical and emotional impacts on quality of life in children & adolescent with hemophilia. It was administered to children & their caregivers. Short version for children containing 16 items (4 to 7 years) and 35 items (8 to <12 years) were selected in this study. This version covers 9 dimensions relevant for children's HRQoL (physical health, feelings, view of yourself, family, friends, other people, sports and school, dealing with hemophilia & treatment). Items were rated along 5 response options: never, seldom, sometimes, often and always, higher scores=greater impairment. Raw score for each domain were transformed to scale ranged between 0 to 100, where lower score=better HRQoL. Haem- A-QoL total score=average of all domain scores and ranged from 0 to 100, where lower scores=better QoL.

Analysis was performed on FAS population. Here, 'number analyzed' = participants with available data for each specified category and '0' in the number analyzed field signifies that no participants were aged 8 to <12 years in arm "BIVV001: Participants aged <6 Years".

Haemo-QoL parent proxy short version: used to measure physical and emotional impacts on quality of life in children and adolescent with hemophilia. It was administered to children & their caregivers. Short version for children's caregivers containing 16 items (participants 4 to 7 years) and 35 items (participants 8 to <12 years) were selected in this study. This version covers 9 dimensions relevant for children's HRQoL (physical health, feelings, view of yourself, family, friends, other people, sports and school, dealing with hemophilia and treatment). Items are rated along 5 response options: never, seldom, sometimes, often and always, higher scores=greater impairment. Raw score for each domain: transformed to scale ranged between 0 to 100, lower score=better HRQoL. Haem-A-QoL total score=average of all domain scores and ranged from 0 to 100, lower scores=better quality of life. Haemo-QoL Total Score as per parent's evaluation was reported in this outcome measure.

Analysis was performed on FAS population. Here, 'number analyzed' = participants with available data for each specified category and '0' in the number analyzed field signifies that no participants were aged 8 to <12 years in arm "BIVV001: Participants aged <6 Years".

Haemo-QoL kids short version: used to measure physical and emotional impacts on quality of life in children and adolescent with hemophilia. It was administered to children and their caregivers. Short version for children containing 35 items (8 to <12 years) were selected in this study. This version covers 9 dimensions considered relevant for the children's HRQoL (physical health, feelings, view of yourself, family, friends, other people, sports and school, dealing with hemophilia and treatment). Items are rated along 5 response options: never, seldom, sometimes, often and always, higher scores=greater impairment. Raw score for physical health domain were transformed to scale ranged between 0 to 100, where lower score=better HRQoL. Change from baseline in physical Health domain score was reported in this outcome measure.

Analysis was performed on FAS population. Here, 'Overall number of participants analyzed' = participants with available data for this outcome measure. Data for this outcome measure was not planned to be collected and analyzed for arm 'BIVV001: Participants aged <6 years'.

Haemo-QoL parent proxy short version: used to measure physical & emotional impacts on quality of life in children & adolescent with hemophilia. It was administered to children & their caregivers. Short version for children's caregivers containing 35 items (participants 8 to <12 years) were selected in this study. This version covers 9 dimensions relevant for children's HRQoL (physical health, feelings, view of yourself, family, friends, other people, sports and school, dealing with hemophilia & treatment). Items are rated along 5 response options: never, seldom, sometimes, often and always, higher scores=greater impairment. Raw score for physical health domain were transformed to scale ranged between 0 and 100, where lower score=better HRQoL. Change from baseline in physical health domain score as per parent's evaluation was reported in this outcome measure.

Analysis was performed on FAS population. Here, 'Overall number of participants analyzed' = participants with available data for this outcome measure. Data for this outcome measure was not planned to be collected and analyzed for arm 'BIVV001: Participants aged <6 years'.

A target joint at Baseline was defined as a major joint with >=3 spontaneous bleeding episodes in a consecutive 6 month period prior to entry to the study, captured at Baseline. A target joint resolved was defined as <=2 spontaneous bleeds into that joint during 12 months of continuous exposure (defined as treatment regimen period >=52 weeks). Total number of target joints resolved at Week 52 were reported.

Analysis was performed on FAS population. Here, 'overall number of participants analyzed' = participants with available data for this outcome measure and had at least 12 months of continuous exposure. 'Overall number of units analyzed' = total number of target joints at Baseline from participants with at least 12 months continuous exposure. Here "0" in 'overall number of participants analyzed' signifies that none of the participants had at least 12 months of continuous exposure.

HJHS is a validated 11-item scoring tool developed for the assessment of joint health in participants with hemophilia. It comprised an evaluation of the elbows, knee and ankle joints: swelling (0 to 3), duration of swelling (0 to 1), muscle atrophy (0 to 2), crepitus on motion (0 to 2), flexion loss (0 to 3), extension loss (0 to 3), joint pain (0 to 2) and strength (0 to 4), in each item 0 = none and higher score = severe damage and global gait (walking, stairs, running, hopping on 1 leg) scored on scale ranged from 0 to 4, where 0 = all skills in normal limit and 4 = no skills within normal limits). Total HJHS score = sum of joint totals (0 to 120) + general gait (1 to 4) and ranged from 0 (no joint damage) to 124 (severe joint damage), where higher score indicated severe joint damage.

Analysis was performed on FAS population. Here, 'overall number of participants analyzed' = participants with available data for this outcome measure.

The Investigators/Surgeons who complete the surgical procedures assess the participant's response to surgery with BIVV001 treatment using a 4-point scale, where responses were categorized as: 1 = Excellent, 2 = Good, 3 = Fair, and 4 = Poor/none. Higher score indicated worst response. This assessment was performed 24 hours after the surgery. A surgery can be counted in more than one response category. As pre-specified, this outcome measure was planned to be analyzed combinedly for both the cohorts (participants <6 years and participants 6 to <12 years) and presented under a single reporting group.

Analysis was performed on a surgery subgroup population which included all participants who had undergone major surgery after the 1st dose of study drug. Here, 'overall number of participants analyzed' = participants with major surgeries during the specified period (defined as the date and time of the first dose of study drug up to the last dose of study drug) and 'overall number of units analyzed' = number of major surgeries during the specified period occurred in participants analyzed.

Perioperative period was time lapse surrounding the surgical act which was divided into 3 stages: preoperative (4 weeks prior to surgery), operative (during the surgery) and post-operative (24-hour post-surgery). The number of injections to maintain hemostasis (process to prevent and stop bleeding from blood vessel) per surgery included all injections from loading dose (i.e., the preoperative injection, administered either on the day of surgery or one day prior to the surgery), to end of surgery. Major surgery: defined as any invasive operative procedure that required any of the following: opening into major body cavity (e.g., abdomen, thorax, skull); operation on a joint; removal of an organ; dental extraction of any molar teeth or >=3 non-molar teeth; operative alteration of normal anatomy; crossing of a mesenchymal barrier (e.g., pleura, peritoneum, dura).

Analysis was performed on surgery subgroup population. Here, 'overall number of participants analyzed' = participants with major surgeries during the specified period and 'overall number of units analyzed' = number of major surgeries during the specified period occurred in participants analyzed. As pre-specified, this outcome measure was planned to be analyzed combinedly for both the cohorts (participants <6 years and participants 6 to <12 years) and presented under a single reporting group.

The perioperative period was the time lapse surrounding the surgical act which was divided into 3 stages: preoperative (4 weeks prior to surgery), operative (during the surgery) and post-operative (24-hour post-surgery). The number of blood component transfusions used during perioperative period were summarized categorically (0, 1, 2, 3 and >3) for all major surgeries for the surgery subgroup. Major surgery: defined as any invasive operative procedure that required any of the following: opening into major body cavity (e.g., abdomen, thorax, skull); operation on a joint; removal of an organ; dental extraction of any molar teeth or >=3 non-molar teeth; operative alteration of normal anatomy; crossing of a mesenchymal barrier (e.g., pleura, peritoneum, dura).

Analysis was performed on surgery subgroup population. Here, 'overall number of participants analyzed' = participants with major surgeries during the specified period and 'overall number of units analyzed' = number of major surgeries during the specified period occurred in participants analyzed. As pre-specified, this outcome measure was planned to be analyzed combinedly for both the cohorts (participants <6 years and participants 6 to <12 years) and presented under a single reporting group.

Perioperative period: time lapse surrounding surgical act which was divided into 3 stages: preoperative (4 weeks prior to surgery), operative (during the surgery) and post-operative (24-hour post-surgery). Total BIVV001 consumption were summarized from the loading dose (the day before surgery, i.e., on Day -1) up to 2 weeks following the surgery (i.e., Day 14) and were reported in this outcome measure.

Analysis was performed on surgery subgroup population. Here, 'overall number of participants analyzed' = participants with major surgeries during the specified period and 'overall number of units analyzed' = number of major surgeries with BIVV001 administration within Day -1 to Day 14. As pre-specified, this outcome measure was planned to be analyzed combinedly for both the cohorts (participants <6 years and participants 6 to <12 years) and presented under a single reporting group.

The perioperative period was the time lapse surrounding the surgical act which was divided into 3 stages: preoperative (4 weeks prior to surgery), operative (during the surgery) and post-operative (24-hour post-surgery). The type of blood component (Red blood cell, platelet, fresh frozen plasma, whole blood and other) transfusions used were summarized for all major surgeries. Post-operative referred to the day following the end of surgery to the date of hospital discharge. Major surgery: defined as any invasive operative procedure that required any of the following: opening into major body cavity (e.g., abdomen, thorax, skull); operation on a joint; removal of an organ; dental extraction of any molar teeth or >=3 non-molar teeth; operative alteration of normal anatomy; crossing of a mesenchymal barrier (e.g., pleura, peritoneum, dura).

Analysis was performed on surgery subgroup population. Here, 'overall number of participants analyzed' = participants with major surgeries during the specified period and 'overall number of units analyzed' = number of major surgeries during the specified period occurred in participants analyzed. As pre-specified, this outcome measure was planned to be analyzed combinedly for both the cohorts (participants <6 years and participants 6 to <12 years) and presented under a single reporting group.

Perioperative period was time lapse surrounding surgical act which was divided into 3 stages: preoperative (4 weeks prior to surgery), operative (during surgery) and post-operative (24-hour post-surgery). Total dose (IU/kg) was sum across all injections per major surgery (including loading dose) needed to maintain hemostasis (process to prevent and stop bleeding from blood vessel) during surgery. Major surgery: defined as any invasive operative procedure that required any of the following: opening into major body cavity (e.g., abdomen, thorax, skull); operation on joint; removal of organ; dental extraction of any molar teeth or >=3 non-molar teeth; operative alteration of normal anatomy; crossing of mesenchymal barrier (e.g., pleura, peritoneum, dura). Day 0=surgery day. Loading dose for given surgery was preoperative injection, administered either on day of surgery or one day prior to surgery (i.e., Day -1).

Analysis was performed on surgery subgroup population. Here, 'overall number of participants analyzed' = participants with major surgeries during the specified period and 'overall number of units analyzed' = number of major surgeries for which a loading dose was given on the day of surgery or one day prior to surgery (i.e. Day -1). As pre-specified, this outcome measure was planned to be analyzed combinedly for both the cohorts and presented under a single reporting group.

The estimated total blood loss (in milliliters) during major surgeries were summarized. Major surgery: defined as any invasive operative procedure that required any of the following: opening into major body cavity (e.g., abdomen, thorax, skull); operation on a joint; removal of an organ; dental extraction of any molar teeth or >=3 non-molar teeth; operative alteration of normal anatomy; crossing of a mesenchymal barrier (e.g., pleura, peritoneum, dura).

Analysis was performed on surgery subgroup population. Here, 'overall number of participants analyzed' = participants with reported blood loss during major surgery and 'overall number of units analyzed' = number of major surgeries with blood loss report during the treatment regimen occurred in participants analyzed. As pre-specified, this outcome measure was planned to be analyzed combinedly for both the cohorts and presented under a single reporting group.

An adverse event (AE) was defined as any untoward medical occurrence in a participant who received study drug which did not necessarily have a causal relationship with the treatment. A serious AE (SAE) was defined as any untoward medical occurrence that at any dose: resulted in death, was life-threatening, required inpatient hospitalization or prolongation of existing hospitalization, resulted in persistent or significant disability or incapacity, was a congenital anomaly or birth defect, or was a medically important event. Treatment-emergent AEs were AEs that developed, worsened or became serious from Baseline (Day 1) up to 3 weeks post last dose.

Analysis was performed on safety analysis set.

Embolic and thrombotic events were defined as arterial or venous thrombosis, confirmed by imaging.

Analysis was performed on safety analysis set.

Cmax was defined as the maximum observed plasma FVIII Activity.

Analysis was performed on PK population which included all participants who had completed adequate blood sample collection to assess key PK parameters. Data was planned to be collected and analyzed for combined population of both arm groups with the available PK data.

CL is defined as the rate at which the drug is removed from the body.

Analysis was performed on PK analysis set. Here, 'overall number of participants analyzed' = participants with available data for this outcome measure. Data was planned to be collected and analyzed for combined population of both arm groups with the available PK data.

Volume of distribution (Vd) is defined as the theoretical volume in which the total amount of drug would need to be uniformly distributed to produce the desired plasma concentration of a drug. Vss is the apparent volume of distribution at steady-state.

Analysis was performed on PK analysis set. Here, 'overall number of participants analyzed' = participants with available data for this outcome measure. Data was planned to be collected and analyzed for combined population of both arm groups with the available PK data.

Plasma t1/2z was the time measured for the plasma concentration of drug to decrease by one half.

Analysis was performed on PK analysis set. Here, 'overall number of participants analyzed' = participants with available data for this outcome measure. Data was planned to be collected and analyzed for combined population of both arm groups with the available PK data.

AUC0-tau was defined as area under the plasma concentration-time profile from time zero (pre-dose) to dosing interval.

Analysis was performed on PK analysis set. Here, 'overall number of participants analyzed' = participants with available data for this outcome measure. Data was planned to be collected and analyzed for combined population of both arm groups with the available PK data.

CLss is defined as the rate at which the drug is removed from the body at steady state.

Data for this outcome measure is not reported because samples were not collected to estimate CLss.

IR was calculated as (Peak activity [in IU/dL] - Trough activity [in IU/dL])/Actual Dose (in IU/kg), and peak activity at each visit was the highest activity level after the dosing, and trough activity at each visit was the activity level prior to the dosing.

Analysis was performed on PK analysis set. Data was planned to be collected and analyzed for combined population of both arm groups with the available PK data.

Ctrough is the pre-dose concentration of a drug. Ctrough was measured by apTT-Baseline-one-stage clotting assay.

Analysis was performed on FAS population. Here, 'number analyzed' = participants with available data for each specified category. Data was planned to be collected and analyzed for combined population of both arm groups with the available PK data.

MRT is the average total time a drug molecule spends in the body.

Analysis was performed on PK analysis set. Here, 'overall number of participants analyzed' = participants with available data for this outcome measure. Data was planned to be collected and analyzed for combined population of both arm groups with the available PK data.

Time above predefined (10% and 40%) FVIII activity levels mean time which BIVV001 maintains above 10 IU/dL and 40 IU/dL with single doses of 50 IU/kg.

Analysis was performed on PK analysis set. Here, 'number analyzed' = participants with available data for each specified category. Data was planned to be collected and analyzed for combined population of both arm groups with the available PK data.

AUC0-tau was defined as the area under the activity-time curve over the dosing interval. AUC was normalized by dose.

Analysis was performed on PK analysis set. Here, 'overall number of participants analyzed' = participants with available data for this outcome measure. Data was planned to be collected and analyzed for combined population of both arm groups with the available PK data.