• tuberculosis

An estimated 1.7 billion people—23% of the world’s population—have been infected by Mycobacterium tuberculosis.1 It has been known for over five decades that, once someone has been infected with M. tuberculosis for more than 2–5 years, the risk of developing tuberculosis (TB) disease—barring a second infection or immunosuppressive condition—is small.2 Nevertheless, numerous publications and textbooks continue to cite a ‘rule of thumb’ that 5% of people with latent TB infection will develop reactivation TB disease after this initial high-risk period. Multiple recent analyses have reaffirmed that this 5% figure is a substantial overestimate.3 4

In this issue of Thorax, Trauer et al reanalyse data from 21 clinical trials of Bacille Calmette-Guérin (BCG) vaccination.5 Their comprehensive analysis provides yet another piece of evidence that the traditional conceptualisation of latent TB infection—as a static state in which people experience a constant, reasonably high risk of reactivation for many years, if not decades—should be abandoned.

Prior analyses have estimated that BCG-derived protection against TB disease may wane after about 10 years,6 though long-term follow-up data are scant. Trauer et al updated a prior meta-analysis of BCG vaccine trials7 to explore whether this waning of protection more likely reflects …