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

Inclusion Criteria:

• Study participant must be 6 to <18 years of age, inclusive, at the time of signingthe informed consent/assent according to local regulation

• Study participant has had a diagnosis of moderate to severe plaque psoriasis (PSO)for at least 3 months prior to the Screening Visit

• Study participant meets the following at both the Screening and Baseline Visits:

1. Body surface area (BSA) affected by PSO ≥10%

2. . Investigator's Global Assessment (IGA) score ≥3 (on a scale from 0 to 4)

3. . Psoriasis Area and Severity Index (PASI) score ≥12 OR

PASI score ≥10 plus at least 1 of the following:

i) Clinically relevant facial involvement ii) Clinically relevant genital involvement iii) Clinically relevant hand and foot involvement

• Study participant is a candidate for systemic PSO therapy and/or photo/chemotherapyand for treatment with ustekinumab per labeling

• Study participant has body weight ≥15 kg and body mass index for age percentile of ≥5 at Screening

Exclusion Criteria:

• Primary failure (no response within 12 weeks) to 1 or more interleukin-17 (IL-17)biologic response modifiers (eg, brodalumab, ixekizumab, secukinumab) OR more than 1biologic response modifier other than an IL-17

• Study participant has a presence of guttate, inverse, pustular, or erythrodermic PSOor other dermatological condition that may impact the clinical assessment of PSO

• Study participant has a history of inflammatory bowel disease (IBD) or symptomssuggestive of IBD

• History of active tuberculosis unless successfully treated, latent TB unlessprophylactically treated

• Study participant has an active infection or history of infections (such as seriousinfection, chronic infections, opportunistic infections, unusually severeinfections)

• Study participant has previously received bimekizumab

• Study participant has previously received ustekinumab

• Study participant has received drugs outside the specified timeframes relative tothe Baseline Visit or receives prohibited concomitant treatments

• Study participant has the presence of active suicidal ideation, or positive suicidebehavior

• Study participant diagnosed with severe depression in the past 6 months (prior toScreening) should be excluded

• Study participant has a history of psychiatric inpatient hospitalization within thepast year before enrolling into the study