A Long-Term Study to Learn About The Study Medicine Called Ritlecitinib in Children With Severe Alopecia Areata.

Study B7981028 is a Phase 3 long-term, double-blind extension study to evaluate the safety and efficacy of ritlecitinib in participants with severe alopecia areata (AA) who have completed previous ritlecitinib studies B7981031 or B7981027 and are eligible to enroll for B7981028 study. The primary objective of this study is to evaluate the long-term safety and tolerability of ritlecitinib in pediatric participants with severe AA who have completed the studies B7981027 or B7981031. The secondary objectives of this study are to evaluate the long-term efficacy of ritlecitinib, durability of response and effect of ritlecitinib on patient centered outcomes. All participants in this study will receive ritlecitinib higher or lower dose for up to an additional 3 years following completion of either of the prior parent studies. Participants who received higher or lower doses in the parent Study B7981027 will continue receiving the same ritlecitinib dose in Study B7981028. Participants who received placebo in the parent Study B7981027 and all participants from parent Study B7981031 will be randomized at a 1:1 ratio to receive higher or lower dose of ritlecitinib in Study B7981028. At least 140 participants evaluable for primary analysis will be enrolled in Study B7981028. Participants will be evaluated for treatment continuation criteria at Months 3 and 6 (for those who were previously assigned to active treatment in parent Study B7981027) and at Months 9 and 12 in Study B7981028 (for those who previously completed Study B7981031 or were assigned to placebo in the parent Study B7981027). Ritlecitinib treatment will be discontinued for any participant who does not meet the study treatment continuation criteria. Safety monitoring will be performed to identify and monitor the known and potential risks of ritlecitinib. The efficacy assessments include Severity of Alopecia Tool (SALT), eyebrow and eyelash assessments. Patient reported outcomes including Patient's Global Impression of Change (PGI-C), Patient-Reported Outcomes Measurement Information System (PROMIS) Parent Proxy - Anxiety Short Form 8a and Depressive Symptoms Short Form 6a, Behavior Rating Inventory of Executive Function®, Second Edition (BRIEF®2), and modified Children's Dermatology Life Quality Index (CDLQI) will be assessed throughout the study.