This is an interventional, randomized, double blind, parallel group, placebo-controlled, Phase 2b, 3-arm study to assess the effect of pegylated-recombinant-human interleukin-2 (rezpegaldesleukin) in adult participants with severe to very severe alopecia areata. The estimated duration includes a screening period of up to 35 days, a 36-week treatment period, an optional 16-week treatment extension period, and a 24-week follow-up period. The maximum study duration is approximately 81 weeks for all participants.