The risk of serious infections associated with vedolizumab in patients with inflammatory bowel disease (IBD) is uncertain. We assessed the risk of serious infections associated with use of vedolizumab versus anti-TNF in patients with IBD, according to IBD subtype and previous exposure to anti-TNF.Based on two U.S. nationwide commercial insurance databases and the French nationwide health insurance database, anti-TNF naïve and experienced patients diagnosed with Crohn's disease (CD) and ulcerative colitis (UC) aged 18 years or older who initiated vedolizumab or an anti-TNF agent after 2010 were identified. Hazard ratios for serious infections comparing vedolizumab and anti-TNF were estimated in propensity score matched cohorts.Among 8768 vedolizumab and 26,656 anti-TNF initiators included after 1:4 variable ratio propensity score matching, 893 serious infections occurred during 37,725 person-years of follow-up. The risk of serious infections was not different between vedolizumab and anti-TNF in the overall IBD cohort (HR, 0.95; 95%CI, 0·79-1.13), while the risk was decreased for vedolizumab users in patients with UC (HR, 0.68; 95%CI, 0·50-0.93), but not CD (HR, 1.10; 95%CI, 0.87-1.38). In patients with UC, vedolizumab was consistently associated with lower risk of serious infections after exclusion of gastrointestinal infections (HR, 0·59; 95%CI, 0.39-0.90).While the risk of serious infections associated with vedolizumab was not different compared to anti-TNF in the overall group of patients with IBD, the risk varied according to IBD subtype, by decreasing in patients with UC, but not CD. These findings may help to clarify the optimal position of vedolizumab in the therapeutic management of IBD.