This study is looking at how well a new medicine called JNJ-78934804 works and how safe it is for people with ulcerative colitis (UC). UC is a condition where the colon, or large intestine, becomes swollen and painful with sores. The study will compare JNJ-78934804 to another medicine called guselkumab over 48 weeks.

Eligibility: To join, you must have had UC for at least 12 weeks and have a specific score on a test called the Mayo score, which measures how active your UC is. You cannot join if your UC is limited to just a small part of the intestine, have other types of colitis, or have had problems with similar medicines before. Pregnant or breastfeeding individuals are also excluded.

• The study lasts 48 weeks, nearly a year.
• Participants should have tried other treatments before.
• Cannot participate if planning to have children soon.

This study could help find new treatments for UC, but it's important to consider the time commitment and eligibility criteria before deciding to join.