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

The purpose of this study is to learn about the safety and effects of the study medicine (called ritlecitinib) for the possible treatment of severe alopecia areata. Alopecia areata is a condition that causes hair loss.

This study is seeking participants who have:

• at least 50% scalp hair loss due to alopecia areata.
• received varicella vaccination (2 doses) or have been infected by varicella zoster virus before based on blood test reports.
• history of clinical response failure to alopecia areata treatment (for children in EU/UK only).

All participants in this study will receive either study medicine (ritlecitinib) or placebo. A placebo does not have any medicine in it but looks just like the medicine being studied.

One-third of participants will receive ritlecitinib higher dose, one-third participants will receive ritlecitinib lower dose, and one-third participants will receive placebo.

The study medicine is a capsule that is taken by mouth. It is taken once each day at home.

The study will compare the experiences of participants receiving ritlecitinib to participants receiving placebo. This will help see if ritlecitinib is safe and effective.

Participants will take part in this study for 6 months. During this time, they will have 8 study visits at the study clinic. The study team will also call participants about 8 times over the phone.

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.