BCG vaccination scar associated with better childhood survival in Guinea-Bissau

Abstract

Background: Recent studies have suggested that Bacille Calmette-Guerin (BCG) vaccination may have a non-specific beneficial effect on infant survival and that a BCG scar may be associated with lower child mortality. No study has previously examined the influence of BCG vaccination on cause of death.

Methods: Two cohorts (A and B) were used to describe the mortality pattern for children with and without BCG scar and to determine specific causes of death. In cohort A (n = 1813), BCG scar was assessed at 6 months of age and as previously described children with a BCG scar had lower mortality over the next 12 months than children with no BCG scar. In cohort B, 1617 children aged 3 months to 5 years of age had their BCG scar status assessed in a household-based survey and mortality was assessed during a 12-month period. Causes of death were determined by verbal autopsy (VA) and related to BCG scar status in a cause-specific hazard function.

Results: Controlling for background factors associated with mortality, there was lower mortality for children with a BCG scar than without in cohort B, the mortality ratio (MR) being 0.45 (95% CI 0.21-0.96). Exclusion of children exposed to TB did not have any impact on the result. In a combined analysis of cohorts A and B, the MR was 0.43 (95% CI 0.28-0.65) controlling for background factors. There were no large differences in distribution of the five major causes of death (malaria, pneumonia, acute diarrhoea, chronic diarrhoea, and meningitis/encephalitis) according to BCG scar status in the two cohorts. Having a BCG scar significantly reduced the risk of death from malaria [MR 0.32 (95% CI 0.13-0.76)].

Conclusions: A BCG scar is a marker of better survival among children in countries with high child mortality. BCG vaccination may affect the response to several major infections including malaria.