Ulcerative Colitis (UC) and Crohn's Disease (CD) are long-term conditions in the gut that can cause diarrhea, swelling (inflammation), bleeding from the anus, and belly pain. The main aim of this study is to check for how many participants with UC and CD signs and symptoms disappear after 3.5 months (14 weeks) of treatment with Vedolizumab (this is called remission).

Participants will be treated with Vedolizumab for approximately 1 year (50 weeks). During the first 1.5 months (6 weeks), participants will receive Vedolizumab as an infusion in the vein (called intravenously). After this, participants will receive Vedolizumab as an injection under the skin (called subcutaneously) for the rest of the treatment. Participants for whom the treatment does not seem to work well after 3.5 months (14 weeks) will stop treatment with Vedolizumab and can change to another treatment and also there will be additional required visits at 6 months (26 weeks) and at 1 year (52 weeks). All participants will be checked again 4.5 months (18 weeks) after their last treatment with Vedolizumab.

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

Inclusion Criteria

To be eligible to participate in this study, participants must meet all the following criteria:

1. In the investigator's opinion, the participant can understand and comply with protocol requirements.

2. The participant signs and dates an electronic informed consent form (ICF) and any required privacy authorization prior to any study procedures.

3. The participant is 18 to 80 years of age at the time of signing the ICF.

4. The participant's immunization is up to date per vedolizumab US prescribing information (USPI).

5. If participant is a woman of childbearing potential (WOCBP):

   1. Agrees to use at least 1 form of highly effective contraception from signing the ICF until at least 18 weeks after the last dose of vedolizumab.
   2. Agrees to avoid donating ova from signing the ICF throughout the duration of the study and for 18 weeks after the last dose of vedolizumab.
   3. Has a negative urine pregnancy test within 3 days before first dose of vedolizumab.
   4. Agrees to forego breastfeeding from first dose of vedolizumab through 18 weeks after the last dose of vedolizumab.

6. If participant is a fertile man:

   1. Agrees to use contraception from signing the ICF until at least 18 weeks after the last dose of vedolizumab
   2. Agrees to avoid donating sperm throughout the study and for 18 weeks after the last dose.

7. The participant has a diagnosis of moderate to severely active UC or CD defined by the following:

   1. CD: A Crohn's Disease Activity Index (CDAI) score of 220 to 450 and a SES-CD >=6 (>=4 if isolated ileal disease) at screening OR
   2. UC: A complete Mayo score (MS) of 6 to 12 with endoscopy subscore of 2 to 3 at screening

8. UC or CD diagnosis established prior to screening by clinical and endoscopic evidence and corroborated by a histopathology report.

9. Demonstrated an inadequate response to, loss of response to, or intolerance of at least one of the following agents: corticosteroids, immunomodulators, and/or advanced therapy.

Exclusion Criteria

Participants who meet any of the following exclusion criteria will be excluded from participation in this study:

1. Received approved or investigational anti-integrin antibodies (i.e., vedolizumab, natalizumab, efalizumab, etrolizumab, abrilumab [AMG 181]) at any time prior to screening.
2. Failed (primary or secondary nonresponse) on more than 2 prior advanced treatments.
3. Use of corticosteroid enemas/suppositories within 2 weeks prior to screening (for UC and CD).
4. In the investigator's opinion the participant meets any contraindication, warnings and precautions, drug interactions, or special population considerations per the vedolizumab USPI, or has (medical history or known allergy, hypersensitivity, or intolerance to vedolizumab or its excipients) (Food and Drug administration [FDA] 2024).
5. Received any investigational biologic therapy <= 6 months prior to screening.
6. The participant has received an advanced treatment for an approved indication other than CD or UC. Advanced therapy include: TNF inhibitors (e.g. infliximab, adalimumab, certolizumab pegol), and IL 12/23 antagonist (e.g. ustekinumab, mirikizumab, risankizumab); and small molecules include JAK inhibitor (e.g. tofacitinib, upadacitinib) and sphingosine-1-phosphate (S1P) receptor modulator (e.g. etrasimod, ozanimod).
7. The participant has any evidence of an active infection during screening.
8. Ileostomy, colostomy, severe, or symptomatic stenosis of the intestine or short bowel syndrome.
9. A surgical procedure requiring general anesthesia within 3 months prior to screening or is planning to or is at risk of undergoing major surgery during the study period.
10. History of malignancy, except for the following: adequately treated nonmetastatic basal cell skin cancer; squamous cell skin cancer that has been adequately treated and that has not recurred for at least 1 year prior to screening; and history of cervical carcinoma in situ that has been adequately treated and that has not recurred for at least 3 years prior to screening. Participants with a remote history of malignancy (example, greater than (>) 10 years since completion of curative therapy without recurrence) will be considered based on the nature of the malignancy and the therapy received; this must be discussed with the sponsor on a case-by-case basis prior to enrollment.
11. History of or symptoms of progressive multifocal leukoencephalopathy (PML) in the investigator's opinion.
12. Has laboratory abnormalities during the screening period.

Takeda provides access to the de-identified individual participant data (IPD) for eligible studies to aid qualified researchers in addressing legitimate scientific objectives (Takeda's data sharing commitment is available on https://clinicaltrials.takeda.com/takedas-commitment?commitment=5). These IPDs will be provided in a secure research environment following approval of a data sharing request, and under the terms of a data sharing agreement.

IPD from eligible studies will be shared with qualified researchers according to the criteria and process described on https://vivli.org/ourmember/takeda/. For approved requests, the researchers will be provided access to anonymized data (to respect patient privacy in line with applicable laws and regulations) and with information necessary to address the research objectives under the terms of a data sharing agreement.