A Study to Evaluate the Efficacy and Safety of Bimekizumab Compared to Ustekinumab in Children and Adolescents From 6 Years to Less Than 18 Years of Age With Moderate to Severe Plaque Psoriasis

The PASI90 response assessments are based on at least 90% improvement in the PASI score from Baseline. This is a scoring system that averages the redness, thickness, and scaliness of the psoriatic lesions (on a 0-4 scale), and weights the resulting score by the area of skin involved. Body divided into 4 areas: head, arms, trunk to groin, and legs to top of buttocks. Assignment of an average score for the redness, thickness, and scaling for each of the 4 body areas with a score of 0 (clear) to 4 (very marked). Determining the percentage of skin covered with PSO for each of the body areas and converting to a 0 to 6 scale. Final PASI= average redness, thickness, and scaliness of the psoriatic skin lesions, multiplied by the involved psoriasis area score of the respective section, and weighted by the percentage of the person's affected skin for the respective section. The minimum possible PASI score is 0= no disease, the maximum score is 72= maximal disease.

The Investigator's Global Assessment (IGA) measures the overall psoriasis severity following a 5-point scale (0-4), where scale 0= clear, no signs of psoriasis; presence of post-inflammatory hyperpigmentation, scale 1= almost clear, no thickening; normal to pink coloration; no to minimal focal scaling, scale 2= mild, just detectable to mild thickening; pink to light red coloration; predominately fine scaling, 3= moderate, clearly distinguishable to moderate thickening; dull to bright red; moderate scaling and 4= severe, severe thickening with hard edges; bright to deep dark red coloration; severe/coarse scaling covering almost all or all lesions.

IGA response (Clear or Almost Clear) is defined as clear [0] or almost clear [1] with at least a two-category improvement from Baseline.

The PASI75 response assessments are based on at least 75% improvement in the PASI score from Baseline. This is a scoring system that averages the redness, thickness, and scaliness of the psoriatic lesions (on a 0-4 scale), and weights the resulting score by the area of skin involved. Body divided into 4 areas: head, arms, trunk to groin, and legs to top of buttocks. Assignment of an average score for the redness, thickness, and scaling for each of the 4 body areas with a score of 0 (clear) to 4 (very marked). Determining the percentage of skin covered with PSO for each of the body areas and converting to a 0 to 6 scale. Final PASI= average redness, thickness, and scaliness of the psoriatic skin lesions, multiplied by the involved psoriasis area score of the respective section, and weighted by the percentage of the person's affected skin for the respective section. The minimum possible PASI score is 0= no disease, the maximum score is 72= maximal disease.

A PASI100 responder is defined as a subject that achieves 100% reduction from Baseline in the PASI score. This is a scoring system that averages the redness, thickness, and scaliness of the psoriatic lesions (on a 0-4 scale), and weights the resulting score by the area of skin involved. Body divided into 4 areas: head, arms, trunk to groin, and legs to top of buttocks. Assignment of an average score for the redness, thickness, and scaling for each of the 4 body areas with a score of 0 (clear) to 4 (very marked). Determining the percentage of skin covered with PSO for each of the body areas and converting to a 0 to 6 scale. Final PASI= average redness, thickness, and scaliness of the psoriatic skin lesions, multiplied by the involved psoriasis area score of the respective section, and weighted by the percentage of the person's affected skin for the respective section. The minimum possible PASI score is 0= no disease, the maximum score is 72= maximal disease.

The PASI90 response assessments are based on at least 90% improvement in the PASI score from Baseline. This is a scoring system that averages the redness, thickness, and scaliness of the psoriatic lesions (on a 0-4 scale), and weights the resulting score by the area of skin involved. Body divided into 4 areas: head, arms, trunk to groin, and legs to top of buttocks. Assignment of an average score for the redness, thickness, and scaling for each of the 4 body areas with a score of 0 (clear) to 4 (very marked). Determining the percentage of skin covered with PSO for each of the body areas and converting to a 0 to 6 scale. Final PASI= average redness, thickness, and scaliness of the psoriatic skin lesions, multiplied by the involved psoriasis area score of the respective section, and weighted by the percentage of the person's affected skin for the respective section. The minimum possible PASI score is 0= no disease, the maximum score is 72= maximal disease.

The Investigator's Global Assessment (IGA) measures the overall psoriasis severity following a 5-point scale (0-4), where scale 0= clear, no signs of psoriasis; presence of post-inflammatory hyperpigmentation, scale 1= almost clear, no thickening; normal to pink coloration; no to minimal focal scaling, scale 2= mild, just detectable to mild thickening; pink to light red coloration; predominately fine scaling, 3= moderate, clearly distinguishable to moderate thickening; dull to bright red; moderate scaling and 4= severe, severe thickening with hard edges; bright to deep dark red coloration; severe/coarse scaling covering almost all or all lesions.

IGA response (Clear or Almost Clear) is defined as clear [0] or almost clear [1] with at least a two-category improvement from Baseline.

A PASI100 responder is defined as a subject that achieves 100% reduction from Baseline in the PASI score. This is a scoring system that averages the redness, thickness, and scaliness of the psoriatic lesions (on a 0-4 scale), and weights the resulting score by the area of skin involved. Body divided into 4 areas: head, arms, trunk to groin, and legs to top of buttocks. Assignment of an average score for the redness, thickness, and scaling for each of the 4 body areas with a score of 0 (clear) to 4 (very marked). Determining the percentage of skin covered with PSO for each of the body areas and converting to a 0 to 6 scale. Final PASI= average redness, thickness, and scaliness of the psoriatic skin lesions, multiplied by the involved psoriasis area score of the respective section, and weighted by the percentage of the person's affected skin for the respective section. The minimum possible PASI score is 0= no disease, the maximum score is 72= maximal disease.

The Investigator's Global Assessment (IGA) measures the overall psoriasis severity following a 5-point scale (0-4), where scale 0= clear, no signs of psoriasis; post-inflammatory hyperpigmentation may be present, scale 1= almost clear, no thickening; normal to pink coloration; no to minimal focal scaling, scale 2= mild, just detectable to mild thickening; pink to light red coloration; predominately fine scaling, 3= moderate, clearly distinguishable to moderate thickening; dull to bright red; moderate scaling and 4= severe, severe thickening with hard edges; bright to deep dark red coloration; severe/coarse scaling covering almost all or all lesions.

IGA 0 response (Clear) is defined as clear [0] with at least a two-category improvement from Baseline.

The Investigator's Global Assessment (IGA) measures the overall psoriasis severity following a 5-point scale (0-4), where scale 0= clear, no signs of psoriasis; post-inflammatory hyperpigmentation may be present, scale 1= almost clear, no thickening; normal to pink coloration; no to minimal focal scaling, scale 2= mild, just detectable to mild thickening; pink to light red coloration; predominately fine scaling, 3= moderate, clearly distinguishable to moderate thickening; dull to bright red; moderate scaling and 4= severe, severe thickening with hard edges; bright to deep dark red coloration; severe/coarse scaling covering almost all or all lesions.

IGA 0 response (Clear) is defined as clear [0] with at least a two-category improvement from Baseline.

An adverse event (AE) is any untoward medical occurrence in a patient or clinical investigation subject administered a pharmaceutical product, which does not necessarily have a causal relationship with this treatment. Treatment-emergent AEs are defined as those AEs that have a start date on or following the first dose of IMP through the final dose of IMP + 20 weeks.

An serious adverse event (SAE) must meet 1 or more of the following criteria:

• Results in death
• Is life-threatening
• Requires inpatient hospitalization or prolongation of existing hospitalization
• Results in persistent disability/incapacity
• Is a congenital anomaly/birth defect
• Important medical event that, based upon appropriate medical judgment, may jeopardize the patient or subject and may require medical or surgical intervention to prevent 1 of the other outcomes listed in the definition of serious.

Treatment-emergent AEs are defined as those AEs that have a start date on or following the first dose of IMP through the final dose of IMP + 20 weeks.

An adverse event (AE) is any untoward medical occurrence in a patient or clinical investigation subject administered a pharmaceutical product, which does not necessarily have a causal relationship with this treatment. Treatment-emergent AEs are defined as those AEs that have a start date on or following the first dose of IMP through the final dose of IMP + 20 weeks. This measure considers any TEAE leading to permanent discontinuation of IMP regardless of reason.

An adverse event (AE) is any untoward medical occurrence in a patient or clinical investigation subject administered a pharmaceutical product, which does not necessarily have a causal relationship with this treatment. Treatment-emergent AEs are defined as those AEs that have a start date on or following the first dose of IMP through the final dose of IMP + 20 weeks. This measure considers any TEAE leading to permanent withdrawal from study.

Safety topics of interest are infections (serious, opportunistic, fungal, and tuberculosis), inflammatory bowel disease, and injection site reactions.

Blood pressure will be measured in millimeters of mercury (mmHg).

Blood pressure will be measured in millimeters of mercury (mmHg).

Pulse rate will be measured in beats per minute (beats/min).

Clinically significant findings or worsening of previous findings since the physical examination at Baseline will be reported as TEAEs.

Growth assessment, as assessed by the change from Baseline in height.

Growth assessment, as assessed by the change from Baseline in weight.

Platelets will be measured in number of platelets per liter (10^9/L).

Erythrocytes will be measured in number of red blood cells per liter (10^12/L).

Hemoglobin will be measured in grams per liter (g/L).

Hematocrit will be measured in volume percentage (%) of red blood cells in blood.

Alkaline phosphatase, alanine aminotransferase, aspartate aminotransferase and gamma-glutamyltransferase will be measured in units per liter (U/L).

Basophils, eosinophils, lymphocytes, monocytes, neutrophils and leukocytes will be measured in number of white blood cells per liter (10^9/L).

Glucose, potassium, sodium and calcium will be measured in millimoles per liter (mmol/L).

Clinical chemistry parameters will be measured in micromols per liter (μmol/L).

The CDLQI is a questionnaire designed to measure the impact of skin diseases on the lives of children. The questionnaire consists of 10 questions that are based on the experiences of children with skin disease. The instrument asks participants about symptoms and feelings, leisure, school or holidays, personal relationships, sleep, and treatment. The questions relate to the impact of the skin disease on the child over the last week. The CDLQI total score ranges from 0 to 30 with higher scores indicating higher impact of skin disease on quality of life (Qol).

The CDLQI is a questionnaire designed to measure the impact of skin diseases on the lives of children. The questionnaire consists of 10 questions that are based on the experiences of children with skin disease. The instrument asks participants about symptoms and feelings, leisure, school or holidays, personal relationships, sleep, and treatment. The questions relate to the impact of the skin disease on the child over the last week. The CDLQI total score ranges from 0 to 30 with higher scores indicating higher impact of skin disease on quality of life (Qol).

The CHAQ is a questionnaire designed to capture physical function in children and adolescents with juvenile rheumatoid arthritis. The CHAQ comprises 2 indices, Disability and Discomfort. The Disability Index assesses the degree of difficulty experienced over the past week across 30 items in the following 8 categories of the daily living activities: dressing and grooming, arising, eating, walking, hygiene, reach, grip, and activities. The Disability Index ranges from 0 (no disability) to 3 (maximum disability). Discomfort is determined by the presence of pain, as measured by a 100-mm visual analogue scale (VAS). In addition, a final global assessment item asks study participants to rate how they are doing by placing a mark on a 100 mm VAS.

The Peak Pruritus NRS measures the worst level of itching in the past 24 hours on an 11-point scale ranging from 0 (no itch) to 10 (worst imaginable itch).

Plasma bimekizumab concentrations prior to investigational medicinal product (IMP) administration and following investigational medicinal product (IMP) administration

Anti-bimekizumab antibody (AbAb) detection prior to investigational medicinal product (IMP) administration and following investigational medicinal product (IMP) administration