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 Full Analysis Set (FAS) consisted of all randomized participants who received at least 1 dose of the study medication and had a valid measurement of the primary efficacy variable at 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; 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.

The Full Analysis Set (FAS) consisted of all randomized participants who received at least 1 dose of the study medication and had a valid measurement of the primary efficacy variable at 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; 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.

The Full Analysis Set (FAS) consisted of all randomized participants who received at least 1 dose of the study medication and had a valid measurement of the primary efficacy variable at Baseline.

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 Full Analysis Set (FAS) consisted of all randomized participants who received at least 1 dose of the study medication and had a valid measurement of the primary efficacy variable at 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.

The Full Analysis Set (FAS) consisted of all randomized participants who received at least 1 dose of the study medication and had a valid measurement of the primary efficacy variable at Baseline.

PASI correlates to the physician's assessment of psoriasis symptoms including redness of lesions, thickness of lesions, scaliness of lesions and extent of disease. Each parameter is graded from 0-4, 0 refers to no disease and 4 to severe involvement. The body is divided into 4 areas for scoring (head, arms, trunk to groin, legs to top of buttocks), and the final score ranges from 0-72. The PASI 100 response rate at Week 12 is measured as the percentage of participants who achieved 100% improvement from baseline PASI at Week 12.

The Full Analysis Set (FAS) consisted of all randomized participants who received at least 1 dose of the study medication and had a valid measurement of the primary efficacy variable at Baseline.

Bimekizumab plasma concentration was expressed in micrograms per milliliter (μg/mL).

Values Below Limit of Quantification (BLQ) were replaced by the value of lower limit of quantification (LLOQ) divided by 2 = 0.075 μg/mL in the calculations of geometric mean and confidence intervals (CIs). Geometric mean was only calculated if at least two-thirds of the concentrations were quantified at the respective time point.

The Pharmacokinetics Per-Protocol Set (PK-PPS) consisted of all randomized participants who took at least 1 dose of the IMP and provided at least 1 quantifiable plasma concentration postdose and had no important protocol deviations affecting the PK variables.

The data were presented as population estimates of CL/F. Given the sparse nature of PK sampling, CL/F cannot be estimated for each treatment group.

It was prespecified in the data analysis plan to combine doses to perform Population PK and PK/PD analysis based on a prior determination that the PK parameters are not dose-dependent.

The PK-PPS consisted of all randomized participants who took at least 1 dose of the IMP and provided at least 1 quantifiable plasma concentration postdose and had no important protocol deviations affecting the PK variables. Given the sparse nature of PK sampling, CL/F cannot be estimated for each treatment group.

The data were presented as population estimates of V/F. Given the sparse nature of PK sampling, V/F cannot be estimated for each treatment group.

It was prespecified in the data analysis plan to combine doses to perform Population PK and PK/PD analysis based on a prior determination that the PK parameters are not dose-dependent.

The PK-PPS consisted of all randomized participants who took at least 1 dose of the IMP and provided at least 1 quantifiable plasma concentration postdose and had no important protocol deviations affecting the PK variables. Given the sparse nature of PK sampling, V/F cannot be estimated for each treatment group.

The data were presented as population estimates of EC50. EC50 was estimated based on all available data and cannot be derived for each treatment arm.

It was prespecified in the data analysis plan to combine doses to perform Population PK and PK/PD analysis based on a prior determination that the PK parameters are not dose-dependent.

The PK-PPS consisted of all randomized participants who took at least 1 dose of the IMP and provided at least 1 quantifiable plasma concentration postdose and had no important protocol deviations affecting the PK variables. EC50 was estimated based on all available data and cannot be derived for each treatment arm.

Antibody positive status prior study treatment was defined as having an antibody level greater than (>) 28.5% at Baseline (Week 0).

The Pharmacokinetics Per-Protocol Set (PK-PPS) consisted of all randomized participants who took at least 1 dose of the IMP and provided at least 1 quantifiable plasma concentration postdose and had no important protocol deviations affecting the PK variables.

Overall antibody positive was defined as having a value of > 28.5% at any time in the Treatment Period. The Treatment Period did not include Baseline/pretreatment samples.

The Pharmacokinetics Per-Protocol Set (PK-PPS) consisted of all randomized participants who took at least 1 dose of the IMP and provided at least 1 quantifiable plasma concentration postdose and had no important protocol deviations affecting the PK variables.

An adverse event (AE) was any untoward medical occurrence in a patient or clinical study participant, temporally associated with the use of investigational medicinal product (IMP), whether or not considered related to the IMP. An AE can therefore be any unfavorable and unintended sign (including an abnormal laboratory finding), symptom, or disease (new or exacerbated) temporally associated with the use of IMP.

The Safety Set (SS) consisted of all participants who received at least 1 dose of the IMP.

An adverse event (AE) was any untoward medical occurrence in a patient or clinical study participant, temporally associated with the use of investigational medicinal product (IMP), whether or not considered related to the IMP. An AE can therefore be any unfavorable and unintended sign (including an abnormal laboratory finding), symptom, or disease (new or exacerbated) temporally associated with the use of IMP.

The Safety Set (SS) consisted of all participants who received at least 1 dose of the IMP.

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

The Safety Set (SS) consisted of all participants who received at least 1 dose of the IMP.

Erythrocytes mean corpuscular hemoglobin (HGB) concentration and hemoglobin were measured in grams per liter (g/L).

The Safety Set (SS) consisted of all participants who received at least 1 dose of the IMP.

Erythrocytes mean corpuscular hemoglobin (HGB) was measured in picograms (pg).

The Safety Set (SS) consisted of all participants who received at least 1 dose of the IMP.

Erythrocytes mean corpuscular volume was measured in femtolitres (fL).

The Safety Set (SS) consisted of all participants who received at least 1 dose of the IMP.

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

The Safety Set (SS) consisted of all participants who received at least 1 dose of the IMP.

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

The Safety Set (SS) consisted of all participants who received at least 1 dose of the IMP.

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

The Safety Set (SS) consisted of all participants who received at least 1 dose of the IMP.

Calcium, chloride, potassium, magnesium, sodium, urea nitrogen, cholesterol and glucose were measured in millimoles per liter (mmol/L).

The Safety Set (SS) consisted of all participants who received at least 1 dose of the IMP.

Lactate dehydrogenase, alkaline phosphatase, alanine aminotransferase, aspartate aminotransferase and gamma glutamyl transferase were measured in units per liter (U/L).

The Safety Set (SS) consisted of all participants who received at least 1 dose of the IMP.

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

The Safety Set (SS) consisted of all participants who received at least 1 dose of the IMP.

C Reactive Protein was measured in milligrams per liters (mg/L).

The Safety Set (SS) consisted of all participants who received at least 1 dose of the IMP.

Urine pH was measured on a pH scale.

The Safety Set (SS) consisted of all participants who received at least 1 dose of the IMP.

Percentages were based on the number of participants with non-missing urinalysis results at Baseline and at Week 12.

The Safety Set (SS) consisted of all participants who received at least 1 dose of the IMP.

Number of participants reflect those with non-missing urinalysis results at Baseline and at Week 12.

Percentages were based on the number of participants with non-missing urinalysis results at Baseline and at Week 12.

The Safety Set (SS) consisted of all participants who received at least 1 dose of the IMP.

Number of participants reflect those with non-missing urinalysis results at Baseline and at Week 12.

Percentages were based on the number of participants with non-missing urinalysis results at Baseline and at Week 12.

The Safety Set (SS) consisted of all participants who received at least 1 dose of the IMP.

Number of participants reflect those with non-missing urinalysis results at Baseline and at Week 12.

Percentages were based on the number of participants with non-missing urinalysis results at Baseline and at Week 12.

The Safety Set (SS) consisted of all participants who received at least 1 dose of the IMP.

Number of participants reflect those with non-missing urinalysis results at Baseline and at Week 12.

Percentages were based on the number of participants with non-missing urinalysis results at Baseline and at Week 12.

The Safety Set (SS) consisted of all participants who received at least 1 dose of the IMP.

Number of participants reflect those with non-missing urinalysis results at Baseline and at Week 12.

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

The Safety Set (SS) consisted of all participants who received at least 1 dose of the IMP.

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

The Safety Set (SS) consisted of all participants who received at least 1 dose of the IMP.

Temperature was measured in degrees Celsius (°C).

The Safety Set (SS) consisted of all participants who received at least 1 dose of the IMP.

The physical examination included general appearance; ear, nose, and throat; eyes, hair, and skin; respiratory; CV; GI; musculoskeletal; hepatic; neurological (including limb reflexes); and mental status.

Any clinically significant abnormal findings during the study were captured as adverse events.

The Safety Set (SS) consisted of all participants who received at least 1 dose of the IMP.

Percentages were based on the number of participants with a non-missing measurement for that variable at the visit.

The Safety Set (SS) consisted of all participants who received at least 1 dose of the IMP.