It's of great importance to effectively induce and maintain disease remission in patients with moderate to severe ulcerative colitis (UC). Vedolizumab (VDZ) is known for its high safety profile and confirmed therapeutic efficacy in UC treatment. However, according to the experience in clinical practice, the effect onset speed of vedolizumab is relatively slow. Upadacitinib (UPA), however, works quickly, which complements the defect of slow onset of VDZ induction. However, the safety of UPA used in situations such as infection and tumors is inferior to that of VDZ, and long-term use requires testing for the risk of adverse events such as deep vein thrombosis. Therefore, if the advantages of long-term maintenance therapy safety of VDZ and rapid induced remission of UPA are fully utilized, the combination of VDZ and UPA induction for 8 weeks, followed by the use of single drug VDZ in maintenance therapy, can maximize the clinical benefits of UC patients. Due to the lack of high-level clinical research data at home and abroad, we plan to conduct a multicenter prospective randomized controlled clinical study to provide the evidence-based basis for the efficacy analysis of the sequential treatment of moderate to severe UC patients with VDZ and UPA.

Inclusion Criteria:

• Diagnosed UC for at least 3 months, including endoscopic evidence supporting UC and histopathological evidence supporting UC diagnosis
• Suffering from moderate to severe UC, defined as modified Mayo score ≥ 4 and endoscopic subscale (ESS) ≥ 2
• Indications for VDZ or UPA application

Exclusion Criteria:

• Patients who are unable to take oral UPA and receive regular intravenous VDZ infusion therapy
• Evidence of toxic megacolon was found during screening
• Previously underwent extensive colectomy, subtotal resection, or total colectomy, ileostomy, or colostomy due to UC
• Subjects who require surgery due to UC or plan to undergo elective surgery during the study period
• There is evidence indicating that the subjects suffer from severe, progressive, or uncontrolled kidney, liver, blood, endocrine, respiratory, mental, or neurological diseases
• Evidence of active hepatitis B or C infection during screening