BCG protects against tuberculosis infection as well as progression from infection to disease, suggests a recent UK study.
The analysis included 14 studies, featuring 3855 participants under the age of 16 years, with selected papers conducted in the UK and Europe, as well as Africa and Asia. Vaccinated and unvaccinated children all had a known recent exposure to patients with pulmonary tuberculosis, and were screened for infection with M.tuberculosis. The exposure to TB ensured that any reduced rate of infection could be attributed to protection by the vaccination. Infection was defined as any positive results of screening, irrespective of whether there was evidence of active TB or not. Disease was defined as presence of active TB, with or without a positive screening result.
Researchers assessed whether BCG vaccination, administered before exposure, was associated with a subsequent negative result on TB screen assay results in participants who had contact with infectious TB. Estimated BCG protection against active disease was also analysed, in a subset of six studies that reported development of active TB from infection.
They found that vaccination led to a significant 19% protective efficacy against TB infection among vaccinated children after exposure to people with TB, compared with unvaccinated children. Protection by BCG against progression from infection to active disease, calculated by using infected individuals, was significant at 58%. Both areas where the policy was to vaccinate at birth, and areas where the children were not vaccinated at birth, found significant protection against infection from BCG vaccination, at 28% and 15% respectively. But the difference between the two were not significant.
The researchers note that ‘given the incomplete control of tuberculosis, especially in high burden countries, optimisation of the use of BCG is sensible’, adding that their analysis ‘provides evidence that BCG protects against TB infection from multiple epidemiologically different settings.’