25/10/04

TB vaccine passes safety tests

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A new tuberculosis (TB) vaccine, designed to work alongside existing immunisation methods, has passed preliminary safety testing, according to findings published in Nature Medicine today (October 25).


TB is highly infectious – the World Health Organisation estimates that about two billion people are currently infected with bacteria that cause TB, and that two million die from the disease every year.


The researchers say that the new vaccine — the first in 80 years — is not intended to replace the existing BCG (Bacillus Calmette-Guérin) jab but rather to complement it, providing an immune boost some months later when the effect of BCG can start to wane.


UK researchers tested the vaccine — called MVA85A — for three years in three different groups; one group had previously been vaccinated with BCG and the other two groups had not.


Of the two groups that had never had BCG, one was given BCG and the other MVA85A. People who had previously been given BCG were given MVA85A as a booster.


The test vaccine was safe, and stimulated a strong immune response both in people who had previously had a BCG dose and in those who had only MVA85A.


Oxford University’s Helen McShane, who led the research team, told SciDev.Net that further tests, “virtually identical” to those completed in the UK, are underway at the Medical Research Council unit in The Gambia.


The reason for the duplication, explains McShane, is that, compared with people in tropical climates such as in Africa where the incidence of TB is high, people in the United Kingdom have little exposure to the bacteria that cause the disease.


Babies in The Gambia — where TB is endemic — are vaccinated with BCG at birth. If the new vaccine shows the same levels of safety and immune response in the Gambian studies as in the UK work, further large-scale efficacy trials will be needed to assess whether the vaccine can prevent disease. However, McShane does not expect the new vaccine to protect against initial infection.


“Data shows that repeated BCG vaccination does not increase protection,” she says. “MVA85A stimulates stronger immune responses that we hope will translate into protection and, if it does, it could be used as a booster at 6 months after the children have been given BCG at birth”.