Mapping the global use of different BCG vaccine strains.

Bacille Calmette-Guérin (BCG) vaccine is one of the oldest and most commonly administered vaccines worldwide. Different BCG vaccine strains exist as a result of genetic changes that occurred during repeated subculture in different countries before lyophilisation was introduced for storage of seed lots in the 1960s. Increasing evidence suggests that these genetically divergent BCG vaccine strains are associated with different protective efficacy against tuberculosis (TB), different rates of adverse events and variable susceptibility to anti-tuberculous drugs. Information on which BCG vaccine strains are used in each country worldwide has not previously been collated. This report summarises data from the EuroTB network and from WHO/UNICEF in the first map depicting the BCG vaccine strains used globally. In 83 (44%) of 188 countries, more than one BCG vaccine strain was used during the five year period. In the countries that used only one strain, BCG Denmark was used in 32, BCG Russia/Bulgaria in 30, BCG Japan in eight, BCG Connaught in two. Twelve countries used their locally-produced BCG vaccine strains. The considerable variation in BCG vaccine strains used worldwide highlights the importance of documenting the particular vaccine strain used on an individual, local and national level. This is important for the interpretation of changes in the epidemiology of adverse events after BCG immunisation, for the management of adverse events after BCG immunisation, to interpret differences in the protective efficacy of BCG, and to inform the design of trials investigating novel TB vaccines.