Additional Study Information: New medical therapy for pediatric Crohn's disease (CD) or pediatric ulcerative colitis (UC). We are currently recruiting pediatric participants (aged 2 to 17 years) who have received a diagnosis of UC or CD but who do not tolerate or respond to standard treatments, including corticosteroids, immunomodulators and TNF-alpha antagonists. The hubble study will be investigating the pharmacokinetics, efficacy, immunogenicity, safety and tolerability of vedolizumab IV, administered by intravenous infusion in pediatric patients. As you may be aware, vedolizumab IV is already approved for use in adults with moderately to severely active UC or CD and has demonstrated significant and clinically relevant evidence of effectiveness in multiple clinical studies. Currently, no clinical data exists in pediatric patients, so this study hopes to investigate the dosing, efficacy and safety profile of vedolizumab IV in younger patients.