Selection and Efficacy-Influencing Factors of First-Line Biologic Agents in Moderate-to-Severe Ulcerative Colitis

Inclusion Criteria: * Age range of 18-70 years old, gender not limited; * According to international guidelines and consensus, patients with ulcerative colitis should be diagnosed to exclude radiation enteritis, infectious enteritis, tumor related diseases, etc; * Patients assessed as moderate to severe ulcerative colitis based on the Mayo score; * During the follow-up period, no relevant treatments (drugs and surgery) were used that could affect the assessment of the efficacy of biologics Exclusion Criteria: * Patients with hemodynamic instability; * Patients with obvious liver and kidney function injury: bilirubin, aminotransferase (ALT, AST) exceeded the upper limit of normal by 2 times; eGFR\<60ml/min or dialysis patients; * Patients allergic to IFX or VDZ; * Patients whose primary disease was gastrointestinal malignancy; * Patients currently suffering from serious or uncontrolled underlying diseases of the blood, digestive tract, metabolism, endocrine, lung, heart, nervous system, mental system, etc.; * Female patients during pregnancy and breastfeeding (including patients with reproductive needs); * Patients with current infection with infectious diseases (hepatitis B, hepatitis C, syphilis, AIDS, tuberculosis, etc.); * Patients who cannot cooperate with regular follow-up and review of laboratory indicators; * Any other circumstances which, in the opinion of the investigator, would render the subject unfit for study inclusion.