How does the level of BCG vaccine protection against tuberculosis fall over time?

WHO estimates that in 2009, 9.4 million people developed tuberculosis and 1.7 million died of the disease worldwide. 1 In the UK, incidence has risen over the past two decades; most cases are in vulnerable groups such as migrants, people who are homeless, or those with a history of imprisonment.2 Bacillus Calmette Guérin (BCG) vaccine offers 70-80% efficacy against severe forms of tuberculosis in childhood, particularly meningitis in infancy.3 4 When given later in life, efficacy against tuberculosis (which, in adults, commonly presents as pulmonary disease) varies in different regions of the world, for reasons that are not clearly understood.3 5 The failure of BCG to protect adults in some populations—in particular in some studies in India6—has sometimes been wrongly generalised to suggest that BCG never protects against pulmonary disease. However, the Medical Research Council trial established that use of BCG in school age children in the UK was highly effective against tuberculosis (80%).7 On the basis of criteria from the International Union Against Tuberculosis and Lung Disease,8 universal BCG vaccination of school children with a negative tuberculin skin test (aimed at preventing the peak of tuberculosis in young adults in the UK) was discontinued in 2005. Current policy recommends vaccination in infancy of children in high risk groups to prevent severe forms of childhood tuberculosis,9 10 and this practice is cost effective