Old vaccines may be better than new
Date: 14.3.2007
Mutations could make recent tuberculosis vaccines less powerful than older ones.
Genetic changes in a commonly used vaccine for tuberculosis could be contributing to its spotty performance, new research suggests.
The results come as researchers race to develop a new and improved vaccine to defend against the burgeoning worldwide epidemic of tuberculosis. The current vaccine — called the Bacillus Calmette-Guerin (BCG) vaccine — has been used since the early 1900s and prevents tuberculosis in most children, but provides inconsistent protection in adults.
The BCG vaccine consists of several strains. They all come from the same source, but were grown in different labs. Stewart Cole of the Pasteur Institute in Paris, France hypothesized that genetic differences acquired during this growth could account for some of the variation in vaccine performance.
To assess this, Cole and his colleagues compared the genomes of ten strains of the BCG vaccine. Their results, published this week in Proceedings of the National Academy of Sciences of the USA, reveal that BCG strains differ in both genomic composition and in gene expression — one vaccine called BCG Pasteur, for example, was lacking 133 genes found in a more recent isolate.1 The researchers then used this genetic information to build a rough family tree of the various strains. They conclude that the older, less commonly used strains — such as BCG Japan — should be genetically closest to the source material for the vaccine, and so should produce more antigenic proteins. ...
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