A Long-Term Extension Study of Vedolizumab in Children and Teenagers With Ulcerative Colitis (UC) or Crohn's Disease (CD)

The main aim of this study is to learn about medical problems (adverse events) if vedolizumab subcutaneously (SC) is given to a child or teenager with UC or CD for a long time. Other aims are to understand if the long time use of vedolizumab SC has an impact on the time period until hospital visits because of bowel swelling (inflammation) are needed and has an impact on the quality of life of children and teenagers who received vedolizumab SC.

In this study, participants who responded well to the treatment with vedolizumab SC in the parent study (VedolizumabSC-3003 \[NCT06100289\]) will continue to be treated with vedolizumab SC. Participants who did not respond well to the treatment with vedolizumab SC in the parent study or who received corticosteroids in the last 4 weeks of the parent study will not receive vedolizumab SC in this study but will be followed for up to 2 years after the last treatment with vedolizumab SC in the parent study.

During the study, participants will visit their study clinic several times.

The drug being tested in this study is Vedolizumab SC. Vedolizumab SC is being tested to treat pediatric participants with moderate to severe active UC or CD. This study will look at the long-term safety profile in pediatric participants who take vedolizumab SC.

The study will enroll approximately 70 participants. This extension study consists of a treatment cohort and an observational cohort. Participants will continue receiving the same dose and frequency of vedolizumab SC that was received at the last dose of the parent study VedolizumabSC-3003 (NCT06100289).

For the Treatment cohort participants will be randomized (1:1) to receive vedolizumab in either a prefilled syringe (PFS) as part of an autoinjector pen (PFS+AI) or a PFS with a needle safety device (PFS+NSD):

* Treatment Cohort: Vedolizumab 108 milligram (mg) PFS+AI
* Treatment Cohort: Vedolizumab 108 mg PFS+NSD

This multi-center trial will be conducted globally. The overall time to participate in this study is up to 2 years from the first dose in the study. Participants in the treatment cohort will have a follow-up safety visit of 18 weeks after their last dose of study drug. Participants who will not be eligible for the treatment cohort will be enrolled in the observational cohort and will be followed for approximately 2 years after the last dose of vedolizumab SC received during Study VedolizumabSC-3003 (NCT06100289).

Eligibility Criteria:
Inclusion Criteria for Treatment Cohort 1. Has completed Week 34 of Study VedolizumabSC-3003 (NCT06100289) and achieved clinical response at Week 34 and was corticosteroid-free for at least the last 4 weeks (Week 30 to Week 34). Clinical response for participants with UC is defined as a reduction of partial Mayo score of \>=2 points and \>= 25 percentage (%) from baseline (from VedolizumabSC-3003 \[NCT06100289\]), including a \>=1-point decrease in the Mayo stool frequency subscore and a \>=1-point reduction in the rectal bleeding subscore or absolute rectal bleeding subscore of less than or equal to (\<=) 1 point. Clinical response for participants with CD is defined as a pediatric Crohn's disease activity index (PCDAI) \<=30 with a reduction in the PCDAI of \>=15 points from baseline (from VedolizumabSC-3003 \[NCT06100289\]).

Inclusion Criteria for Observational Cohort

1. Has received at least 1 dose of vedolizumab during Study VedolizumabSC-3003 (NCT06100289) and early terminated OR completed the Week 34 clinic visit of Study VedolizumabSC-3003 (NCT06100289) but was not eligible to enroll in the treatment cohort of this study.

Exclusion Criteria for Treatment Cohort

1. Has hypersensitivity or allergies to vedolizumab or any of its excipients.
2. The participant currently requires major surgical intervention for UC or CD (example, bowel resection), or is anticipated to require major surgical intervention for UC or CD during the study.