TB vaccines "could spread infection"

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."

Copyright PA Business 2008