Older versions of the bacille Calmette-Guérin (BCG) vaccine used to immunize against tuberculosis may be more effective than some of the more recent strains, according to a new study by French researchers (Brosch R et al. Proc Natl Acad Sci U S A. doi:10.1073/pnas.0700869104 [published online ahead of print March 19, 2007]).
The BCG vaccine has been in use since the early 1900s; the researchers speculated that various daughter strains derived from this source have accumulated genetic mutations affect immunogenicity. When they compared the genomes of different BCG daughter strains, they found extensive genetic changes, especially in newer strains, that could compromise the vaccine's efficacy. They also noted that a 2006 study found that newborns vaccinated with BCG Japan, an “early” strain, had more powerful immune responses than newborns vaccinated with a “late” strain, BCG Danish (Davids V et al. J Infect Dis. 2006;193:531-536).
Stephenson J. TB Vaccine. JAMA. 2007;297(15):1646. doi:10.1001/jama.297.15.1646-c