A Study to Learn About the Safety of Vedolizumab and How Well it Works in Children and Teenagers With Active Chronic Pouchitis

When some people have their large bowel removed, a surgeon can make a "pouch" from part of the small bowel to connect it to the back passage (anus). Pouchitis is when the pouch becomes inflamed (swollen) or infected. The main aim of this study is to find out if vedolizumab improves pouchitis symptoms and pouch inflammation. Other aims include to find out if vedolizumab is well tolerated and if it causes any medical problems (adverse events or side effects) and to look for any changes in the well-being of participants during their treatment with vedolizumab. This study consists of two parts: Part 1 includes the induction and maintenance periods, and Part 2 includes the continued maintenance period. Participants will receive up to 12 infusions of vedolizumab. In Part 1 of the study, first 3 infusions are in first 6 weeks (Day 1, Week 2 and Week 6). Participants who are getting benefit may continue with the treatment for up to 7.5 months (30 weeks) in the maintenance period for Part 1. After completing treatment with vedolizumab in Part 1, participants will visit their clinic for a health check at Week 34. Participants who show clinical response at Week 34 will continue to Part 2, receiving vedolizumab every 8 weeks for an additional 40 weeks, starting at Week 38 and ending with the last dose being at Week 78. Final efficacy assessments, including a pouchoscopy will be performed at Week 82.

The drug being tested in this study is called vedolizumab. This study will look at the efficacy, safety, tolerability, pharmacokinetics (PK), and immunogenicity of vedolizumab in pediatric participants with active chronic pouchitis. The study will enroll approximately 30 participants. All the participants will be enrolled in a single treatment group to receive treatment with vedolizumab based on participant's weight mentioned as follows: * Participants with body weight greater than or equal to (\>=) 30 kilogram (kg) will receive vedolizumab, high dose * Participants with body weight greater than (\>) 15 to less than (\<) 30 kg will receive vedolizumab, medium dose * Participants with body weight 10 to 15 kg will receive vedolizumab, low dose All participants will receive vedolizumab intravenous infusion at Day 1, and at Weeks 2, 6, 14, 22, and 30. Participants will also receive concomitant antibiotic treatment (ciprofloxacin, metronidazole, or other antibiotics) from Day 1 through Week 2. Participants with clinical response at the end of Part 1 maintenance at Week 34 will continue to Part 2 of the study and will receive vedolizumab intravenous infusion every 8 weeks from Week 38 through Week 78. This multi-center trial will be conducted globally. The maximum overall duration of the study is up to approximately 2 years. Participants will be followed up for 18 weeks after the last dose of the study drug for safety.