A Study to Assess the Pharmacokinetics and Safety of Bimekizumab in Children and Adolescents With Moderate to Severe Hidradenitis Suppurativa

Inclusion Criteria: * Study participant must be 12 to \<18 years of age at the time of informed consent/assent, at Tanner stage 2 or more, for the first 8 participants only, followed by also including participants ≥9 to \<18 years of age at Tanner stage 2 or more. * Study participant must have a diagnosis of HS for at least 6 months prior to the Baseline Visit. * Study participant must have moderate to severe HS, defined as a total of ≥5 inflammatory lesions (ie, the sum of abscesses and inflammatory nodules), as assessed at both the Screening and Baseline Visits. * Study participant must have HS lesions present in at least 2 distinct anatomic areas, 1 of which must be at least Hurley Stage II or III, as assessed at both the Screening and Baseline Visits. * Study participant must have had a history of inadequate response to a course of a systemic antibiotic for treatment of HS * Study participant must weigh ≥30kg at the Screening Visit. Exclusion Criteria: * Study participant has a draining tunnel count of \>20 at either the Screening or Baseline Visits. * Study participant has experienced primary failure (no response within 12 weeks) to 1 or more IL 17 biologic response modifiers (eg, brodalumab, ixekizumab, secukinumab) OR primary failure to more than 1 biologic response modifier other than an IL-17 biologic response modifier. * Study participant has previously participated in this study or has received previous therapy with bimekizumab. * Study participant has a history of IBD or symptoms suggestive of IBD. * History of active tuberculosis unless successfully treated, latent TB unless prophylactically treated * Study participant has an active infection or history of infections (such as serious infection, chronic infections, opportunistic infections, unusually severe infections) * Study participant has received drugs outside the specified timeframes relative to the Baseline Visit or receives prohibited concomitant treatments * Study participant has the presence of active suicidal ideation, or positive suicide behavior, * Study participant diagnosed with severe depression in the past 6 months prior to the Screening Visit. * Study participant has a history of psychiatric inpatient hospitalization within the past year before enrolling into the study.