Vedolizumab Intravenous (IV) Dose Optimization in Ulcerative Colitis

The drug being tested in this study is called Vedolizumab. Vedolizumab will be administered as an IV infusion. It is being tested in this study with new doses. This study will investigate the efficacy and safety of dose optimization of vedolizumab IV, compared with standard dosing of vedolizumab IV, over a 30-week treatment period. The study will enroll approximately 250 moderately to severely active subjects with UC in order to randomize approximately 100 non-responder subjects with high vedolizumab drug clearance. Subjects will receive induction therapy of vedolizumab IV 300 mg on Day 1 and Week 2 (Lead-in Period). At Week 5, serum vedolizumab concentration will be measured. At Week 6, subjects will be assessed for clinical response based on partial Mayo score. Results of both Week 5 vedolizumab concentration and Week 6 clinical response will determine the treatment pathway. Those who are non-responders based on partial Mayo score at Week 6 and who are assessed as having high vedolizumab clearance, based on a predefined Week 5 serum vedolizumab concentration threshold (\<50 microg/mL) will be randomly assigned (by chance, like flipping a coin) to one of the two treatment groups: * Vedolizumab IV Standard Treatment * Vedolizumab IV Dose Optimized All randomized subjects will receive vedolizumab IV either 300 mg or 600 mg every 4 or 8 weeks. This multi-center trial will be conducted in United States of America and Canada. The overall time to participate in this study is 56 weeks. Subjects will make multiple visits to the clinic, and will be contacted by telephone, 6 months after last dose of study drug for a long term follow-up safety survey.