This clinical trial is focused on studying the long-term safety and effectiveness of a medication called Ozanimod for treating a condition known as Ulcerative Colitis. Ulcerative Colitis is a chronic disease that causes inflammation and sores in the lining of the large intestine, which can lead to symptoms like abdominal pain and diarrhea. The medication being tested, Ozanimod, is taken orally in the form of a hard capsule and is known by the code name RPC1063.

The purpose of this study is to determine whether long-term use of Ozanimod is safe and effective for people with moderate to severe Ulcerative Colitis. Participants in the study will take Ozanimod over an extended period, and researchers will monitor their health to see how well the medication works and if there are any side effects. Some participants may receive a placebo, which is a substance with no active medication, to compare the effects of Ozanimod.

Throughout the study, participants will have regular check-ups to assess their condition and any changes in their symptoms. The study aims to gather information on how many patients experience improvements, such as clinical remission, which means the symptoms of Ulcerative Colitis are reduced or disappear. The study will also look at other factors like endoscopic improvement, which involves examining the inside of the colon to see if there is less inflammation, and whether patients can achieve remission without the use of corticosteroids, a type of medication often used to reduce inflammation.