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Friday 10th October 2008
TB vaccinations could actually spread the lung infection by clearing the way
for tougher strains to flourish, a new study has claimed.
Vaccinating against tuberculosis might simply remove a weak form of the
infection, allowing a virulent strain to break out, researchers from the
University of Bristol found.
Nearly nine million new cases of TB break out every year, with nearly two
million deaths worldwide. Efforts to create a vaccine have created more than 200
candidates, many of which are currently undergoing animal testing and early
clinical trials.
Large-scale genetic analysis of strains of TB mycobacteria have shown they are
more varied than first thought and that vaccines may be effective against only
some of the circulating strains.
Dr Caroline Colijn, from Bristol's department of engineering and maths, devised
several models to replicate how these various strains would react to certain
drugs.
She said: "In most scenarios increasing vaccine coverage reduces the overall TB
burden. However, the benefits are reduced if the preferential removal of one
strain allows a previously suppressed strain to succeed.
"We found that there is a possibility that TB prevalence may increase due to a
vaccination programme effective against a dominant strain, if that strain didn't
provoke a good immune response."
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