The purpose of this clinical trial is to learn about long-term safety and long-term effects of the study medicine (called ritlecitinib) for the potential treatment of severe alopecia areata, a condition that causes hair loss.
This study is seeking participants who have:
* previously completed one of Pfizer's pediatric studies for Alopecia Areata (B7981027 or B7981031). * at least 50% scalp hair loss due to alopecia areata (for participants enrolling from the study B7981031). * received varicella vaccination (2 doses) or have been infected by varicella zoster virus before based on blood test reports.
All participants in this study will receive the study medicine (ritlecitinib). Participants who received ritlecitinib higher or lower doses in the parent Study B7981027 will continue receiving the same ritlecitinib dose in this trial.
Participants who received placebo in the parent Study B7981027 and all participants from parent Study B7981031 will receive either higher or lower dose of ritlecitinib in this trial.
The study medicine is a capsule that is taken by mouth. It is taken 1 time each day at home.
The study will help see if ritlecitinib is safe and effective. Participants will take part in this study for a duration of up to 3 years (36 months). During this time, they will have 17 study visits at the study clinic. The study team will also call participants once a month over the phone.
Participants with alopecia areata (AA) (including alopecia totalis [AT] and alopecia universalis [AU]) who completed the studies B7981027 or B7981031.
For participants originating from Study B7981031: At least 50% scalp hair loss due to AA (ie, a SALT score of ≥50) at both the Screening and Baseline visits.
Exclusion criteria for participants originating from Study B7981027 with ≤ 30 Days between last dose in Study B7981027 and first visit of Study B7981028
During Study B7981027 or in the period between the last dose of study intervention in Study B7981027 and the first dose of study intervention of Study B7981028, presence of safety events that would require permanent discontinuation based on the B7981028 protocol.
Study participants discontinued from Study B7981027 due to issues other than safety-related events and considered by the investigator for enrolment in Study B7981028 must have resolution of the issue(s) resulting in discontinuation from the parent study prior to enrolment in Study B7981028.
Exclusion criteria for participants originating from Study B7981031 or from Study B7981027 with >30 Days between last dose in Study B7981027 and first visit of Study B7981028