Different Bacillus Calmette-Guerin (BCG) vaccine strains may have different non-specific effects

We assessed the effect of two BCG strains (Danish and Russian) on childhood morbidity and BCG scarification in Guinea-Bissau.

During 2011-2013, infants in the Bandim Health Project’s study area received the Danish or Russian BCG in a natural experiment. Health center consultations were registered at point of care and scar status and size at age 4½ months. We assessed the effect of strain on consultation rates between vaccination and age 45 days, and the effect of BCG strain on prevalence and size of BCG scar.

Among 1206 children, 18% received Danish BCG and 82% Russian BCG. The adjusted hazard ratio (aHR) for consultations was 0.94 (95% CI 0.60 -1.46) for Danish BCG compared with Russian BCG. Girls vaccinated with Danish BCG tended to have lower consultation rates compared with girls vaccinated with Russian BCG (aHR 0.56 (0.25-1.24)), whereas the effect was opposite for boys (aHR 1.24 (0.74-2.11), p=0.09 for interaction between strain and sex). Children vaccinated with Danish BCG were more likely to develop a scar (97%) than children vaccinated with Russian BCG (87%), the relative risk being 1.11 (1.06-1.16)). The effect was stronger in girls, and BCG scar size was larger among infants vaccinated with the Danish strain. 

BCG strain influences scar prevalence and scar size, and may have sex differential effects on morbidity. BCG strains are currently used interchangeably, but BCG scarring has been linked to subsequent survival. Hence, more research into the health effects of different BCG strains is warranted. Small adjustments of BCG production could potentially lower childhood morbidity and mortality at low cost.