This clinical trial is focused on studying the effects of a medication called Risankizumab in people with Ulcerative Colitis. Ulcerative Colitis is a chronic condition that causes inflammation and sores in the lining of the large intestine. The study aims to evaluate how effective and safe Risankizumab is as a maintenance treatment for individuals with moderate to severe Ulcerative Colitis who have previously responded to an initial treatment with Risankizumab.

Participants in the study will receive either Risankizumab or a placebo. The study is divided into several parts. In the first part, the focus is on comparing Risankizumab with a placebo to see how well it works in maintaining the health of participants over a period of time. In the second part, the study will look at two different ways of adjusting the dose of Risankizumab to see which method is more effective. The third part of the study will continue to monitor the long-term safety of Risankizumab in participants who have completed the earlier parts of the study or who were unable to complete the final examination due to external factors like the COVID-19 pandemic or geopolitical issues.

The study will last for a total of 52 weeks, during which participants will be monitored for any changes in their condition. The goal is to see if Risankizumab can help maintain remission, which means the symptoms of Ulcerative Colitis are reduced or disappear. The study will also look at other factors like improvements in the lining of the intestine and overall quality of life. Participants will be closely observed to ensure their safety throughout the study.