Newer TB vaccines are losing their effectiveness and older versions may have to be brought back, say French researchers.
Recent forms of the Bacillus Calmette Guerin (BCG)jab work very well in children, but the protection they afford adults varies from 0 to 80%, depending on country, say the researchers.
They said genetic changes in the newer BCG versions have resulted in more variability and have weakened their potency.
Research published last year showed that an older Japanese strain prompted a greater degree of protection in babies than a newer Danish strain.
Newer versions account for two thirds of the 335 million doses injected worldwide, and were developed because they produced fewer side effects.
PNAS online (2007