To describe the association between Bacille Calmette-Guérin (BCG) vaccination and IDDM development in two different case-control series (A and B) in Montreal.
Case-control series A comprised 93 IDDM cases and 2,903 control subjects who participated in a community-based tuberculin reactivity survey and who belonged to the same birth cohorts and areas of residence as the IDDM cases, Case-control series B comprised 249 IDDM cases and 431 age- and sex-matched friends and neighborhood control subjects.
In series A, the BCG vaccination prevalence among cases and control subjects was 21.5% (95% CI 13.2–29.8%) and 22.3% (95% CI 20.8–23.8%), respectively. The odds ratio (OR) for IDDM associated with BCG vaccination was 1.09 (95% CI 0.62–1.91), after adjusting for the birth cohorts and areas of residence. The vaccination prevalence in series B was 17.7% (95% CI 13.0–22.4%) among cases and 15.1% (95% CI 11.7–18.5%) among control subjects. The OR for IDDM due to BCG vaccination was 1.26 (95% CI 0.79–2.02), taking into account the matched sets. Only one case (3.3%) from series B who had been vaccinated at birth was diagnosed by age 5, compared with 52 cases (24.5%) who had not been vaccinated (P < 0.01).
The lower proportion of birth-vaccinated IDDM cases diagnosed at a very young age, compared with nonvaccinated cases, possibly reflects a temporary boost of the immune functions after vaccination. However, as a whole, results from these analyses fail to support a protective role of BCG vaccination against juvenile-onset IDDM.