Inclusion Criteria:

• Male or female subjects, aged 2 to 17 years (inclusive), who weigh ≥ 10 kg at the time of screening and enrollment into the study.
• Subjects with moderately to severely active UC diagnosed at least 1 month before screening, defined by a modified Mayo score of 5 to 9 (sum of Mayo endoscopic subscore, stool frequency subscore, and rectal bleeding subscore) with a Mayo endoscopic subscore of ≥2 (mucosal friability indicates an endoscopic subscore of at least 2).
• Subjects who have failed, lost response to, or been intolerant to treatment with at least 1 of the following agents:
  • corticosteroids, immunomodulators (e.g., azathioprine, 6-mercaptopurine, methotrexate), and/or TNF-α antagonist therapy (e.g., infliximab, adalimumab). This includes subjects who are dependent on corticosteroids to control symptoms and who are experiencing worsening of disease when attempting to wean off corticosteroids.
• Subjects with evidence of UC extending proximal to the rectum (i.e., not limited to proctitis), at a minimum.
• Subjects with extensive colitis or pancolitis of > 8 years’ duration or left-sided colitis of > 12 years’ duration must have documented evidence of a negative surveillance colonoscopy within 12 months before screening.
• Subjects with vaccinations that are up-to-date based on the countrywide, accepted schedule of childhood vaccines.

Exclusion Criteria:

• Subjects who have had previous exposure to approved or investigational anti-integrins including, but not limited to natalizumab, efalizumab, etrolizumab, or AMG 181, or mucosal addressin cell adhesion molecule-1 antagonists or rituximab.
• Subjects who have had prior exposure to vedolizumab.
• Subjects with hypersensitivity or allergies to any of the vedolizumab excipients.
• Subjects who have received either:
  • an investigational biologic (other than those listed in the first Exclusion Criterion bullet above) within 60 days or 5 half-lives before screening (whichever is longer); or
  • an approved biologic; or
  • biosimilar agent within 2 weeks before the first dose of study drug or at any time during the screening period.
• Subjects with active cerebral/meningeal disease, signs/symptoms or history of progressive multifocal leukoencephalopathy (PML) or any other major neurological disorders including stroke, multiple sclerosis, brain tumor or neurodegenerative disease.
• Subjects who currently require surgical intervention or are anticipated to require surgical intervention for UC during this study.
• Subjects who have had subtotal or total colectomy or have a jejunostomy, ileostomy, colostomy, ileo-anal pouch, or known fixed stenosis of the intestine.
• Subjects with a current diagnosis of indeterminate colitis.
• Subjects with clinical features suggesting monogenic very early onset inflammatory bowel disease.