A Study to Learn About Medicine Called Ritlecitinib in Children Aged Between 6 to 12 Years With Severe Alopecia Areata

Study B7981027 is being conducted to assess efficacy and safety of ritlecitinib in pediatric participants 6 to \<12 years of age with severe AA. The primary objective of this study is to evaluate the efficacy of ritlecitinib compared to placebo in pediatric participants with severe AA on regrowth of lost scalp hair. The secondary objectives are to evaluate safety, tolerability, acceptability and palatability of ritlecitinib and to evaluate the effect of ritlecitinib on patient centered outcomes. This study will have 3 treatment arms, including 2 ritlecitinib dosage levels (higher and lower doses) and 1 placebo arm. The participants will be assessed for study eligibility at the screening visit after informed consent/assent is obtained (as applicable). Participants will receive study medication for a duration of 24 weeks. At least 225 participants will be enrolled in the study. At least 30% of total study population will be recruited from Europe. 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), Alopecia Areata Patient Priority Outcomes (AAPPO), 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. Pharmacokinetics of ritlecitinib will be evaluated using sparse sampling. Safety monitoring will be performed to identify and monitor the known and potential risks of ritlecitinib. Participants completing the 24-week treatment period of the study may have the option to enter the long-term extension (LTE) Study B7981028, if the eligibility criteria are met. Participants who complete the 24-week treatment period of the study but who are ineligible for the LTE study will undergo a 4-week off-treatment follow-up period.