⁃ For Treatment Cohort:

• The participant should have completed Study MLN0002-3024 or Study MLN0002-3025 and achieved corticosteroid-free clinical response at Week 54 (and has tapered off of steroids, as applicable, at least 12 weeks before Week 54) as defined by a reduction of partial Mayo score of ≥2 points and ≥25% from baseline for participants with UC, or by a decrease of pediatric Crohn's disease activity index (PCDAI) of ≥15 points for participants with CD and with total PCDAI ≤30.

• A male participant who is sexually active with a female partner of childbearing potential agrees to use a barrier method of contraception (e.g., condom with or without spermicide) from signing of participant/parental informed consent and/or pediatric assent throughout the duration of the study and for 18 weeks after last dose. The female partner of a male participant should also be advised to use a highly effective method of contraception.

• A female participant of childbearing potential who is sexually active with a nonsterilized male partner agrees to use a highly effective method of contraception from signing of participant/parental informed consent and/or pediatric assent throughout the duration of the study and 18 weeks after the last dose.

⁃ For Observational Cohort:

⁃ 1\. The participant has received at least 1 dose of vedolizumab during Study MLN0002-3024 or Study MLN0002-3025 and early terminated OR completed the Week 54 visit of Study MLN0002-3024 or Study MLN0002-3025 but was not eligible to enroll in the treatment cohort of this study.