The lower Hb and iron levels prevalent in sub-Saharan Africa (due to a combination of factors including genetics and malnutrition)59 may contribute to the poor protective efficacy of BCG vaccination in this population if BCG is unable to replicate efficiently, while haemolysis-inducing diseases could act to boost BCG growth and immunogenicity by increasing availability of free Hb. Here, GSTM1 is linked to nutritional deficiency disease.