Abstract
OBJECTIVESParaguay 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 Guérin [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.METHODSWe 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).RESULTSAfter controlling for age, gender, education, occupation and marital status, the OR of BCG scar on the risk of leprosy was 0.10 (95% confidence interval [CI], 0.02 to 0.45), for an estimate of vaccine effectiveness of 89.5% reduced risk of leprosy (95% CI, 55.2 to 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 SF had a p<0.05), and both the RERI and SF indicated a less then multiplicative and additive interaction of BCG and younger age.CONCLUSIONSBCG vaccination was associated with a decreased risk of leprosy in the study population, particularly in persons born after 1980.
Highlights
We reviewed the scientific literature using an Ovid MEDLINE for the period 1946 and the week ending on June 5, 2021, searching the terms Bacillus of Calmette and Guérin (BCG) vaccine and leprosy in combination with clinical trials, experimental studies in humans, cohort, case-control, cross-sectional and ecologic or epidemiologic studies and found 111 references, from which 30 were epidemiologic studies, and none of them was conducted in Paraguay
The most striking difference was on the presence of BCG scar: odds ratio (OR), 0.2; 95% confidence interval (CI), 0.1 to 0.5; p= 0.001)
In a population at high-risk of leprosy, located in one of the three countries with the heaviest burden of leprosy in the Americas, we found a decreased risk of leprosy conferred by BCG vaccination
Summary
Based on the evidence of a meta-analysis [2] that included data from 5 randomized trials, 6 cohort studies and 17 case-control studies with a pooled 59% effectiveness (95% confidence interval [CI], 34 to 84), the 2017 WHO SAGE report concluded that “in comparison to the effectiveness of BCG against (tuberculosis), BCG seems to be more protective against leprosy” [1]. As noted in the same report, a BCG trial conducted in Bangladesh reported in 0.4% of contacts receiving the vaccine developed clinical leprosy within 12 weeks of the immunization with BCG [3]. A recent survey conducted by the WHO Global Leprosy Program found that few leprosy-endemic countries have adopted the use of BCG or revaccination of contacts of leprosy cases, including Brazil, Colombia and Peru in the Americas [4].
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