Association between Bacillus Calmette-Guérin (BCG) vaccination and inflammatory bowel disease: A two-stage sampling design within the Quebec Birth Cohort on Immunity and Health (CO·MMUNITY).

Background: Bacillus Calmette-Guérin (BCG) vaccination, primarily administered to prevent tuberculosis, exhibits nonspecific immune effects and could play a role in inflammatory bowel disease prevention. We investigated the associations of BCG with Crohn's disease and ulcerative colitis, and assessed sex-differences.

Methods: This two-stage study included 365,206 Canadians from the Quebec Birth Cohort on Immunity and Health (1970-2014; stage 1). Vaccination status was registry-based and inflammatory bowel disease cases were identified from health services with validated algorithms. We documented additional factors among 2644 participants in a nested case-control study in 2021 (stage 2). A two-stage logistic regression analysis was applied to estimate the odds ratios (OR), corrected for sampling fractions and adjusted for confounding factors. We used interaction terms to assess sex-differences on the multiplicative scale.

Results: In the stage 1 sample, 2419 cases of Crohn's disease and 1079 of ulcerative colitis were included. Forty-six percent of non-cases received the BCG vaccine as compared to 47% for Crohn's disease and 49% for ulcerative colitis. Associations differed by sex. BCG vaccination was not associated with Crohn's disease among men (OR = 0.91; 95% CI: 0.79-1.04) but was related to an increased risk among women (OR = 1.13; 95% CI: 1.00-1.28, P interaction: 0.001). For ulcerative colitis, there was a tendency toward a slightly elevated risk among men (OR = 1.09; 95%CI: 0.90-1.32), whereas the risk was more substantial for women (OR = 1.17; 95% CI:0.99-1.39, P interaction: <0.001).

Conclusion: BCG vaccination does not play a preventive role in inflammatory bowel disease. Our results point to distinct associations between men and women.