Is the efficacy of the BCG vaccine so poor? No.
- BCG vaccine efficacy ranges widely from none to high in different populations.
- BCG is derived from Mycobacterium bovis; TB is caused by Mycobacterium tuberculosis.
- Both are members of the bacterial genus Mycobacterium.
- Majority of Mycobacterial species are saprophytes, i.e. harmless organisms existing in soil and water.
- Such saprophytic mycobacteria are called NTM (Non-Tuberculous Mycobacteria).
- NTM prevalence influences BCG vaccine efficacy, i.e. higher the prevalence of and exposure to NTM , lower the vaccine efficacy of BCG.
- Reasons for this NTM effect not yet fully understood. Either masks or blocks BCG effect. Masks as in NTM itself protects, nothing for BCG to add. Blocks as in prevents BCG from eliciting effective immunity.
From Fine, Paul EM. “Variation in protection by BCG: implications of and for heterologous immunity.” The Lancet 346.8986 (1995): 1339-1345.
Is BCG not really administered anymore? On the contrary.
- A picture speaks louder than words. The current BCG vaccine administration map shows most of the world’s population is either currently covered (very light orange) by universal BCG vaccination or used to be (purple).
- Currently, only Belgium, Canada, Italy, the Netherlands and USA do not recommend universal BCG vaccine (dark orange).