A Study to Assess the Pharmacokinetics, Safety, and Efficacy of Two Doses of Bimekizumab in Adolescent Study Participants With Moderate to Severe Plaque Psoriasis

Percentage of Participants With Treatment-emergent Adverse Events (TEAEs)

An adverse event (AE) is any untoward medical occurrence in a patient or clinical study participant, temporally associated with the use of IMP, whether or not considered related to the IMP. Treatment-emergent AEs are defined as those AEs that started date on or following the first dose of IMP through the final dose of IMP +20 weeks. The last dose was given 4 weeks prior end of extension period.

Time frame: From day of first dose (Week 0) through 20 weeks after final dose of IMP (up to Week 140)]

Percentage of Participants With Serious Treatment-emergent Adverse Events

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 started date on or following the first dose of IMP through the final dose of IMP +20 weeks. The data was rounded to one decimal place. The last dose was given 4 weeks prior end of extension period.

Time frame: From day of first dose (Week 0) through 20 weeks after final dose of IMP (up to Week 140)

Percentage of Participants With Treatment-emergent Adverse Events (TEAEs) Leading to Discontinuation of Investigational Medicinal Product (IMP)

An AE is any untoward medical occurrence in a patient or clinical study participant, temporally associated with the use of IMP, whether or not considered related to the IMP. Treatment-emergent AEs are defined as those AEs that started 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. The last dose was given 4 weeks prior end of extension period.

Time frame: From day of first dose (Week 0) through 20 weeks after final dose of IMP (up to Week 140)

Percentage of Participants With Treatment-emergent Adverse Events (TEAEs) Leading to Withdrawal From the Study

An AE is any untoward medical occurrence in a patient or clinical study participant, temporally associated with the use of IMP, whether or not considered related to the IMP. Treatment-emergent AEs are defined as those AEs that started date on or following the first dose of IMP through the final dose of IMP +20 weeks. This measure considers any TEAEs leading to withdrawal from the study. The last dose was given 4 weeks prior end of extension period.

Time frame: From day of first dose (Week 0) through 20 weeks after final dose of IMP (up to Week 140)

Exposure-adjusted Incidence Rates (EAIR) of Selected Safety Topics of Interest

Selected safety topics of interest (including infection \[serious, opportunistic, fungal, and tuberculosis (TB)\], inflammatory bowel disease \[IBD\], and injection site reactions) with onset occurring from day of first dose through 20 weeks after final dose of IMP adjusted by duration of participant exposure to IMP. The exposure-adjusted incidence rate (EAIR) is defined as the number of participants (n) with a specific AE adjusted for the exposure and was scaled to 100 participant-years. The last dose was given 4 weeks prior end of extension period.

Time frame: From day of first dose (Week 0) through 20 weeks after final dose of IMP (up to Week 140)

Change From Baseline in Vital Signs (Systolic and Diastolic Blood Pressure)

Blood pressure was measured in millimeters of mercury (mmHg).

Time frame: Baseline (Week 0), Weeks 16, 124, Safety Follow-Up (up to Week 140)

Change From Baseline in Vital Signs (Pulse Rate)

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

Time frame: Baseline (Week 0), Weeks 16, 124, Safety Follow-Up (up to Week 140)

Change From Baseline in Vital Signs (Temperature)

Temperature (oral, axillary, otic or non-contact forehead) was measured in degrees Celsius (°C).

Time frame: Baseline (Week 0), Weeks 16, 124, Safety Follow-Up (up to Week 140)

Change From Baseline in Hematology Parameters (Platelet Count)

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

Time frame: Baseline (Week 0), Weeks 16, 124, Safety Follow-Up (up to Week 140)

Change From Baseline in Hematology Parameters (Mean Corpuscular Hemoglobin)

Mean corpuscular hemoglobin (HGB) was measured in picograms (pg).

Time frame: Baseline (Week 0), Weeks 16, 124, Safety Follow-Up (up to Week 140)

Change From Baseline in Hematology Parameters (Mean Corpuscular Volume)

Mean corpuscular volume was measured in femtolitres.

Time frame: Baseline (Week 0), Weeks 16, 124, Safety Follow-Up (up to Week 140)

Change From Baseline in Hematology Parameters (Erythrocytes)

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

Time frame: Baseline (Week 0), Weeks 16, 124, Safety Follow-Up (up to Week 140)

Change From Baseline in Hematology Parameters (Hemoglobin)

Hemoglobin was measured in grams per liter.

Time frame: Baseline (Week 0), Weeks 16, 124, Safety Follow-Up (up to Week 140)

Change From Baseline in Hematology Parameters (Hematocrit)

Hematocrit was measured in volume percentage (%) of red blood cells in the blood.

Time frame: Baseline (Week 0), Weeks 16, 124, Safety Follow-Up (up to Week 140)

Change From Baseline in Clinical Chemistry Parameters (Alkaline Phosphatase, Alanine Aminotransferase, Aspartate Aminotransferase)

Alkaline phosphatase, alanine aminotransferase, aspartate aminotransferase was measured in units per liter.

Time frame: Baseline (Week 0), Weeks 16, 124, Safety Follow-Up (up to Week 140)

Change From Baseline in Hematology Parameters (Basophils, Eosinophils, Lymphocytes, Monocytes, Neutrophils, Leukocytes)

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

Time frame: Baseline (Week 0), Weeks 16, 124, Safety Follow-Up (up to Week 140)

Change From Baseline in Clinical Chemistry Parameters (Calcium, Potassium, Sodium, Blood Urea Nitrogen, Glucose (Nonfasting)

Calcium, potassium, sodium, blood urea nitrogen, and glucose (non fasting) was measured in millimoles per liter (mmol/L).

Time frame: Baseline (Week 0), Weeks 16, 124, Safety Follow-Up (up to Week 140)

Change From Baseline in Clinical Chemistry Parameters (Creatinine, Total and Direct Bilirubin)

Creatinine and bilirubin was measured in micromols per liter (μmol/L).

Time frame: Baseline (Week 0), Weeks 16, 124, Safety Follow-Up (up to Week 140)

Change From Baseline in Clinical Chemistry Parameters (Total Protein)

Total protein was measured in gram per liter (g/L)

Time frame: Baseline (Week 0), Weeks 16, 124, Safety Follow-Up (up to Week 140)

Change From Baseline in Height

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

Time frame: Baseline (Week 0), Weeks 16, 124

Change From Baseline in Weight

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

Time frame: Baseline (Week 0), Weeks 16, 124

Percentage of Participants With Psoriasis Area and Severity Index (PASI) 90 Response at Week 16

Percentage of participants with PASI 90 response at Week 16 is reported. PASI90 response assessments are based on at least 90% improvement in PASI score from Baseline. This is scoring system that averages redness, thickness, and scaliness of psoriatic lesions(on a 0-4 scale), and weights resulting score by area of skin involved. Body divided into 4 areas:head, arms, trunk to groin, and legs to top of buttocks. Assignment of average score for redness, thickness, and scaling for each of 4 body areas with score of 0(none) to 4(very marked). Determining percentage of skin covered with psoriasis(PSO) for each of body areas and converting to 0 to 6 scale. Final PASI=average redness, thickness, and scaliness of psoriatic skin lesions, multiplied by involved PSO area score of respective section, and weighted by percentage of person's affected skin for respective section. Minimum possible PASI score is 0=no disease, maximum score is 72=maximal disease. Data was rounded to one decimal place.

Time frame: Week 16

Percentage of Participants With Investigator's Global Assessment (IGA) 0/1 (Clear [0]/Almost Clear [1] With at Least 2-category Improvement From Baseline) Response at Week 16

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 thickening, pink to light red coloration and predominately fine scaling, 3= moderate, clearly distinguishable to moderate thickening; dull to bright red, clearly distinguishable to moderate thickening; moderate scaling and 4= 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 data was rounded to one decimal place.

Time frame: Week 16

Percentage of Participants With Psoriasis Area and Severity Index (PASI) 75 Response at Week 4

Percentage of participants with PASI75 response at Week 4 is reported. PASI75 response assessments are based on at least 75% improvement in PASI score from Baseline. This is scoring system that averages redness, thickness, and scaliness of psoriatic lesions (on a 0-4 scale), and weights resulting score by 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 redness, thickness, and scaling for each of 4 body areas with a score of 0 (clear) to 4 (very marked). Determining percentage of skin covered with PSO for each of body areas and converting to 0 to 6 scale. Final PASI=average redness, thickness, and scaliness of psoriatic skin lesions, multiplied by involved psoriasis area score of respective section, and weighted by percentage of person's affected skin for respective section. Minimum possible PASI score is 0=no disease, maximum score is 72=maximal disease. Data was rounded to one decimal place.

Time frame: Week 4

Percentage of Participants With Anti-bimekizumab Antibody (AbAb) Detection Prior to Investigational Medicinal Product (IMP) Administration

Anti-bimekizumab antibody (AbAb) detection prior to IMP administration. Anti-bimekizumab antibodies was measured using 3-tiered assay approach: screening assay, confirmatory assay, and titration assay. Antidrug antibody (ADAb) positive status: any sample that is positive screen and positive immunodepletion (regardless of availability of a titer value). ADAb negative status: any sample that is either negative screen, or positive screen and negative immunodepletion, and where the bimekizumab concentration is less than or equal to the drug tolerance limit of the validated ADAb assay. ADAb missing status: any sample that is either negative screen or positive screen and negative immunodepletion and where the bimekizumab concentration exceeds the validated ADAb assay drug tolerance limit.

Time frame: Baseline (Week 0)

Percentage of Participants With Anti-bimekizumab Antibody (AbAb) Detection Following Investigational Medicinal Product (IMP) Administration

Anti-bimekizumab antibody (AbAb) detection following IMP administration. Overall ADAb positive is defined as having at least one sample that is confirmed positive following the 1st dose of IMP to SFU (regardless of missing data). Overall ADAb negative is defined as having all samples reported as negative, or has only one missing/inconclusive sample, following the 1st dose of IMP to SFU. Overall ADAb missing if the study participant has more than one missing ADAb sample for any reason and all other available ADAb samples are negative. The data was rounded to one decimal place.

Time frame: From Baseline (Week 0, post-first dose) to Safety Follow-Up (Week 140)

Change From Baseline in Children's Dermatology Life Quality Index (CDLQI) Response at Week 16

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, (ie, over the last 7 days). The CDLQI total score ranges from 0 to 30 with higher scores indicating higher impact of skin disease on quality of life (Qol).

Time frame: Baseline, Week 16