Long-term Safety With Vedolizumab Intravenous (IV) in Pediatric Participants With Ulcerative Colitis (UC) or Crohn's Disease (CD)

The purpose of this study is to determine the safety profile of long-term vedolizumab IV treatment in pediatric participants with UC or CD.

The drug being tested in this study is called Vedolizumab. Vedolizumab is being tested to treat pediatric participants who have moderately to severely active UC or CD.

This study will look at the long-term safety profile in participants who take vedolizumab IV. Participants will continue receiving the same dose assigned from the parent study MLN0002-2003 \[NCT03138655\], which will remain blinded until week 40.

The dosing regimen selected for the long-term study is intended to maintain clinical response at the lowest possible exposure.

At the discretion of the investigator, participants receiving the low dose (150 or 100 milligram \[mg\]) of vedolizumab IV may be escalated to the high dose (300 or 200 mg) if the participants demonstrate disease worsening at 2 consecutive visits (scheduled or unscheduled).

Participants who experience continued disease worsening during the study despite being administered vedolizumab 300 or 200 mg every 8 weeks (Q8W) will be discontinued from the study.

Study duration will be until vedolizumab IV is commercially available for pediatric indication(s) in the participant's country or until other drug access programs become available (whichever comes first), the participant turns 18 years of age and can be transitioned to commercial drug, the participant withdraws from the study, or the sponsor decides to close the study (up to approximately 8 years).

Eligibility Criteria:
Inclusion Criteria:

1. Is male or female with UC or CD and was between 2 to 17 years, inclusive, at the time of randomization for Study MLN0002-2003.

   (Note: A participant remains eligible to participate in this study after they reach 18 years of age if they continue to meet the inclusion criteria and do not meet any exclusion criteria.)
2. Has completed Study MLN0002-2003 and, at Week 22, achieved clinical response as defined by a reduction of partial Mayo score of \>=2 points and \>=25% from Baseline, or a reduction of the Paediatric Ulcerative Colitis Activity Index (PUCAI) of \>=20 points from baseline for participants with UC; or a reduction of the CDAI as defined by a \>=70-point decrease from Baseline or a decrease of Pediatric Crohn's Disease Activity Index (PCDAI) of \>=15 points for participants with CD.
3. May be receiving a therapeutic dose of the following drugs:

   * Oral 5-aminosalicylic acid (5-ASA) compounds.
   * Oral corticosteroid therapy (prednisone or equivalent steroid at a dose less than or equal to \[\<=\] 50 milligram per day \[mg/day\]) provided the participant was receiving this medication during prior participation in MLN0002-2003.
   * Topical (rectal) treatment with 5-ASA or corticosteroids.
   * Probiotics (example, Saccharomyces boulardii).
   * Antidiarrheals (example, loperamide, diphenoxylate with atropine) for control of chronic diarrhea.
   * Antibiotics used for the treatment of CD (i.e., ciprofloxacin, metronidazole).
   * Azathioprine (AZA) or 6-mercaptopurine (6-MP) or methotrexate (MTX), provided the participant was receiving this medication during prior participation in MLN0002-2003.
4. The participant's vaccinations are up to date as per inclusion criteria number 10 in MLN0002-2003.

Exclusion Criteria:

1. Is female and is lactating or pregnant.
2. Has hypersensitivity or allergies to vedolizumab or any of its excipients.
3. Has withdrawn from Study MLN0002-2003.
4. Has developed any new unstable or uncontrolled cardiovascular, heart failure moderate to severe (New York Class Association III or IV), pulmonary, hepatic, renal, gastrointestinal (GI), genitourinary, hematological, coagulation, immunological, endocrine/metabolic, neurological, or other medical disorder that, in the opinion of the investigator, would confound the study results or compromise participant safety.
5. Has a positive progressive multifocal leukoencephalopathy (PML) subjective symptom checklist prior to the administration of the first dose of study drug.
6. 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.
7. Has other serious comorbidities that will limit his or her ability to complete the study.