Phase 3b Study to Assess the Efficacy, Safety, and Tolerability of Remibrutinib in Comparison to Placebo, With Omalizumab as Active Control, in Adult CSU Patients, Followed by an Open-label 52-week Optional Extension.

The study consists of 4 periods, and the total study duration is up to 112 weeks. Approximately 468 adult participants with CSU are expected to be randomized in the study. Screening period: A screening period of up to 4 weeks will allow for the assessment of eligibility, determination of baseline disease activity and wash-out of prohibited medications. Core Phase Treatment Period (52 weeks): The treatment period will be double-dummy and double-blind, with placebo injections matching omalizumab 300 mg s.c. given to participants in the remibrutinib arm and placebo tablets matching remibrutinib 25 mg given to participants in the omalizumab arm (double-dummy). At the randomization visit, eligible participants will be randomized to one of four treatment arms. Extension Phase Treatment Period (52 weeks): Optional open-label extension where patients receive treatment with open-label remibrutinib 25 mg, for 52 weeks. Follow-up period: For patients that do not enter the extension phase, there will be a 16-week, treatment-free, safety follow-up period. Patients that enter extension phase will have a 4-week treatment-free safety follow-up period at the end of the extension phase. All participants will be on a stable, local label-approved standard dose of a second-generation H1-AH ("background therapy") throughout the entire core phase (starting a minimum of 7 days prior to randomization until the end of the core phase). In addition, to treat unbearable symptoms of CSU flare-ups, participants will be allowed to use a different second-generation H1-AH on an as-needed basis ("rescue therapy").