Fig. 2. Historical phylogeny of BCG vaccine strains. Continuous passage of the original strain attenuated by Calmette and Guérin resulted in a number of diverse daughter strains.

Loss of the genomic region of difference 1 (RD1) generated the early Bacillus Calmette–Guérin (BCG) strains (groups I and II). Late strains (groups III and IV) were subsequently generated by deletion of RD2. Adapted from Brosch et al.²⁵, PNAS. Copyright (2007) National Academy of Sciences, USA.