Abstract BACKGROUND Infliximab (IFX) is the only FDA-approved intravenous therapy for the treatment of pediatric inflammatory bowel disease (IBD). The gut-selective anti-integrin vedolizumab (VDZ) has been increasingly used as second-line therapy. However, the comparative effectiveness of IFX vs. VDZ to treat biologic-naïve children with IBD is currently unknown. AIMS 1. Compare the real-world effectiveness of IFX vs. VDZ in bio-naïve pediatric patients with IBD at 12 months. 2. Study the safety of IFX and VDZ in the pediatric population. METHODS A single-center retrospective cohort study was conducted at an academic children’s hospital between February 2015 and August 2023. We included bio-naive mild-moderate IBD patients, <23 years old, who started IFX or VDZ as their first advanced therapy. Patients with a confirmed diagnosis of IBD based on Porto criteria with baseline and at least 6-month follow-up data were included. Exclusion criteria were designed to limit the study population to patients who would typically be eligible for vedolizumab treatment according to the current standard of care, including: prior biologic use; steroid-refractory acute-severe colitis; stricturing or penetrating Crohn’s disease (CD); or perianal disease; and extraintestinal manifestations. The primary outcome was steroid-free clinical remission (SFCR) at 12 months, defined by the PUCAI <10 or ShPCDAI <10 and off corticosteroids. Biochemical remission (BR) was defined as fecal calprotectin (FCP) <250 μg/g. Descriptive statistics included the Chi-square and the Mann-Whitney U test. RESULTS Among the 100 included patients, 73 in IFX group vs. 27 in VDZ group, the mean age was 13 ± 4 years old, males were 68% (IFX) vs. 41% (VDZ) (P = 0.01). 49% had CD, 48% had UC, and 3% had unclassified IBD (IBDU). IFX- and VDZ-treated patients had similar Paris classifications. Baseline albumin levels (3.7 vs. 4.2 g/L, P<0.01) and steroid use (58% vs. 74%, P = 0.13) were lower in IFX vs. VDZ-treated patients. 12-month SFCR was 72% (49/68) and 71% (15/21) in IFX- and VDZ-treated patients, respectively (NS). Among SFCR at 12 months, BR was 59.62% (IFX) vs. 76.47% (VDZ), P = 0.21. Adverse events were rated as mild to moderate and occurred rarely in 8.22% (6/73) of IFX patients and in 7.41% (2/27) of VDZ patients (P = 0.89). These included an infusion reaction (1 in each group), elevated liver enzymes (1 in each group), infection (1), folliculitis (1), eczema (1), , and psoriasis (1). CONCLUSION We found both IFX and VDZ to have similar effectiveness in achieving SFCR and BR at 12 months when used as first-line agents for patients with uncomplicated mild-moderately active IBD. Prospective, larger head-to-head studies are needed for further validation. IFX group vs. VDZ group at the baseline. IFX group vs. VDZ group for Steroid Free Clinical Remission Patients at 12 months.