Early BCG vaccination is unrelated to pulmonary immunity against Mycobacterium tuberculosis in adults

To the Editor: Vaccination with Mycobacterium bovis bacille Calmette–Guerin (BCG) is performed for the prevention of tuberculosis. M. bovis BCG vaccination is among the most commonly applied of all vaccines worldwide [1]. M. bovis BCG vaccination efficiently reduces the morbidity and mortality of tuberculosis in children, especially miliary tuberculosis and meningitis [2]. Although recent investigations of Mycobacterium tuberculosis -specific immune responses by interferon-γ release assays (IGRAs) provide evidence on the effect of M. bovis BCG vaccination on the prevention of primary infection with M. tuberculosis [3–5], it has been suggested that this effect diminishes during adolescence [2, 6]. Consequently, adults are probably not protected from pulmonary tuberculosis by BCG vaccination. To date, no study has investigated the impact of M. bovis BCG vaccination performed in childhood on pulmonary immune responses in adults. The objective of this study was to assess the effect of childhood M. bovis BCG vaccination on systemic and pulmonary immune responses to M. tuberculosis in healthy adult individuals exposed to patients with acid-fast bacilli (AFB)-positive sputum smear-positive tuberculosis in Germany. An observational, cross-sectional, multicentre study was conducted by the German Ministry of Education and Research-funded research consortium on “Pulmonary Tuberculosis – Host and Pathogen Determinants of Resistance and Disease Progression (TB or Not TB)”. Healthcare workers (HCWs) with 1) ongoing professional contact with patients with AFB sputum smear-positive tuberculosis, 2) a cumulative professional exposure of at least 2 years, and 3) no clinical signs and/or symptoms of active tuberculosis were recruited at 18 German pulmonary medicine centres (centres are listed in the Acknowledgements section). Furthermore, household contacts (HHCs) without evidence of active tuberculosis were enrolled at three urban municipal healthcare centres ( i.e. Frankfurt, Hamburg and Hannover); their enrolment required 1) the absence of clinical signs and/or …