International study suggests benefits of TB vaccine have been underestimated

The BCG vaccine used to prevent tuberculosis (TB) has a bigger role in protecting children than previously thought, according to an international study led by investigators at Imperial College London and published in the American Journal of Respiratory and Critical Care Medicine. BCG was understood to prevent severe illness from tuberculosis, but not to prevent infection with TB bacteria. Now data collected from five countries in Europe suggest that the vaccine is also effective at preventing infection.

The BCG vaccine is made from a weakened form of bacteria closely related to human TB. The vaccine is 70-80 per cent effective against the most severe forms of TB, such as TB meningitis in children. In the UK, it is not given as part of the routine childhood vaccination schedule unless a baby is thought to have an increased risk of coming into contact with TB.

TB is the second biggest killer, after HIV/AIDS, out of all infectious diseases worldwide. It is caused by bacteria called Mycobacterium tuberculosis that infect the lungs, but people can be infected for years without showing any symptoms. This latent infection can be treated using a long course of antibiotics, but the most widely-used diagnostic test, the tuberculin skin test, can give false positive results in people who have had a BCG vaccine. This makes it difficult to establish whether BCG protects against infection using this test.

In the last decade, a new blood test called the interferon gamma release assay (IGRA) has been introduced, enabling latent TB infection to be diagnosed more accurately.

The new study, by a network of paediatricians from Europe called ptbnet, analysed skin test and blood test results from 1,128 children in Greece, Spain, Italy, Bulgaria and the UK to establish whether BCG prevents TB infection. The researchers also looked to address questions about the reliability of these tests and how they should be used in children.

The results show that children who had the BCG vaccine were over 50 per cent less likely to show evidence of infection with the blood test, suggesting that BCG doesn't just prevent severe disease but also protects against TB infection.