There are about 10 million cases of TB globally each year and 1 in 3 people are infected with the TB bacterium. BCG is the most widely used vaccine worldwide, but its mechanism of protection is poorly understood. It is thought to prevent progression of infection to active TB but whether it protects against the acquisition of infection itself has not been investigated in humans. The effect of BCG vaccine has been difficult to ascertain because, until recently, the century-old tuberculin skin-prick test (TST) was the only method for detecting infection. However, TST cannot reliably distinguish between TB infection and BCG vaccination. In this study researchers used the more accurate T-cell based blood test called the ELISpot and TST to assess infection.
Ajit Lalvani (Wellcome Trust Senior Clinical Research Fellow, University of Oxford, UK) and colleagues investigated risk factors for TB infection in 979 children from Istanbul, Turkey. All children taking part shared a household with at least one adult with TB. 770 of the children had a BCG scar. The researchers found that the absence of a BCG scar was a strong, independent risk factor for infection in TB-exposed children, while the presence of a BCG scar was associated with a 24% reduction in risk of being infected. The authors state that this finding furthers our understanding of the biology of TB transmission and has important implications for the development of new TB vaccines.
Dr Lalvani states: "Contrary to prevailing theory that BCG vaccination protects only against tuberculosis disease, our results suggest that the vaccine also protects against tuberculosis infection…Our findings show that children can be protected against TB infection by vaccination and this opens a new door for the development of new, improved vaccines." (Quote by e-mail; does not appear in published paper)
See also accompanying comment.
Contact: Dr Ajit Lalvani, Nuffield Department of Clinical Medicine, University of Oxford, Level 7,John Radcliffe Hospital, Headley Way, OXFORD, OX3 9DU, UK. T) +44 (0) 7767 700 873 ajit.lalvani@ndm.ox.ac.uk
Journal
The Lancet