Comparison of the efficacy of liquid and freeze-dried strains of B.C.G. vaccine in preventing tuberculosis.

Analysis of the tuberculosis notifications and the statistics of B.C.G. vaccinations among 13-year-old schoolchildren in Birmingham, England, between 1953 and 1969 shows that the Copenhagen strain of B.C.G. (liquid batches issued 1953-61) and the Glaxo Laboratories strain (freeze-dried batches issued 1962-68) were of similar high efficacy in the prevention of tuberculosis. The method of analysis could be used for the surveillance of the protective efficacy of B.C.G. vaccine in other population groups where it is used routinely but not universally.