BCG growth variation can modulate the immune response to BCG

In Guinea-Bissau we found that during a period when the manufacturer experienced slow growth rate of the BCG vaccine, the BCG vaccine was actually much better at inducing a BCG scar and a positive tuberculin skin test response.

These indicators are all positively associated with improved survival in childhood.  Hence, variations in the production of BCG vaccine may influence important immunological effects of the vaccine

Biering-Sørensen S, et al. Variation of growth in the production of
the BCG vaccine and the association with the immune response. An observational
study within a randomised trial. Vaccine. 2015 Mar 10. pii:
S0264-410X(15)00245-5. doi: 10.1016/j.vaccine.2015.02.056.