A Study With a Initial Treatment Period Followed by a Randomized-withdrawal Period to Evaluate the Efficacy and Safety of Bimekizumab in Adult Subjects With Moderate to Severe Chronic Plaque Psoriasis

Inclusion Criteria: * Must be at least 18 years of age * Chronic plaque psoriasis (PSO) for at least 6 months prior to the Screening Visit * Psoriasis Area Severity Index (PASI) \>=12 and body surface area (BSA) affected by PSO \>=10% and Investigator's Global Assessment (IGA) score \>=3 on a 5-point scale * Subject is a candidate for systemic PSO therapy and/or phototherapy * Female subject of child bearing potential must be willing to use highly effective method of contraception Exclusion Criteria: * Subject has an active infection (except common cold), a recent serious infection, or a history of opportunistic, recurrent, or chronic infections * Subject has concurrent acute or chronic viral hepatitis B or C or human immunodeficiency virus (HIV) infection * Subject has known tuberculosis (TB) infection, is at high risk of acquiring TB infection, or has current or history of nontuberculous mycobacterium (NTMB) infection * Subject has any other condition, including medical or psychiatric, which, in the Investigator's judgment, would make the subject unsuitable for inclusion in the study * Presence of active suicidal ideation or positive suicide behavior * Presence of moderately severe major depression or severe major depression * Subject has any active malignancy or history of malignancy within 5 years prior to the Screening Visit EXCEPT treated and considered cured cutaneous squamous or basal cell carcinoma, or in situ cervical cancer