Objectives: Paraguay has experienced a 35% reduction in the detected incidence of leprosy during the last ten years, as the vaccination coverage against tuberculosis (Bacillus of Calmette and Guerin [BCG] vaccine) reached ≥95% among infants. The objective of this case-control study was to evaluate the protective effect of BCG on the risk of leprosy.
Methods: We used a population-based case-control study of 20 leprosy confirmed cases reported among residents of Ciudad del Este, Paraguay, diagnosed in 2016-2017. Three controls were selected from a random sample of households from the city. We assessed vaccine effectiveness using 1- odds ratio [OR], and confounding for age, gender, education, occupation, and marital status using stratified and exact logistic regression, and explored if there was effect modification calculating the synergy factor (SF) and relative excess risk due to interaction (RERI).
Results: After controlling for age, gender, education, occupation and marital status, the odds ratio of BCG scar on the risk of leprosy was 0.105 (95% CI = 0.019, 0.448), for an estimate of vaccine effectiveness of 89.5% reduced risk of leprosy (95% CI = 55.2%, 98.1%). There was evidence of heterogeneity by which the effectiveness of BCG seemed stronger among younger persons (Breslow-Day and Z-test of the synergy factor had a p = 0.03), and both the RERI and SF indicated a less then multiplicative and additive interaction of BCG and younger age.
Conclusion: BCG vaccination was associated with a decreased risk of leprosy in the study population, particularly in persons born after 1980.
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