This program consists of 3 separate studies: a 48-week Phase 2 dose-ranging study (GALAXI 1) and two 48-week Phase 3 confirmatory studies (GALAXI 2 and GALAXI 3). In Phase 2, safety and efficacy of guselkumab dose regimens will be evaluated to support the selection of induction and maintenance dose regimens for confirmatory evaluation in Phase 3. Participants who complete the 48-week Phase 2 or Phase 3 studies may be eligible to enter the long term extension (LTE). Throughout the 3 studies, efficacy, pharmacokinetic, biomarkers, and safety will be assessed.