Revisiting the Chingleput BCG vaccination trial for the impact of BCG revaccination on the incidence of tuberculosis disease.

Background & objectives: Vaccines play a crucial role in the prevention of tuberculosis (TB). Revaccination with Bacille Calmette-Guerin (BCG) for the prevention of TB is an important strategy that is currently gaining interest. The objective of this study was to reanalyze the community-based Chingleput BCG vaccination trial for protective efficacy of BCG revaccination against incident TB disease. Methods: A retrospective analysis of the Chingleput BCG vaccination trial (conducted in 1968) data was carried out. Data on participants with evidence of prior BCG vaccination at trial intake and randomized to BCG vaccine [low dose (0.01 mg), high dose (0.1 mg)] and placebo arms were analyzed. The incidence of TB disease, which was based on sputum culture and/or chest X-ray was compared between the BCG and placebo arms over a 15 yr follow up period. Results: Of the 269,727 individuals randomized in the trial; 263,158 had no evidence of TB at baseline, of which 4436 (1.68%) had evidence of BCG vaccination at trial intake (2890 in the BCG vaccine and 1546 in the placebo arms, respectively). There were 77 (190 per 100,000) and 64 (296 per 100,000) incident TB cases in the BCG and placebo arm, respectively, at 15 yr post-vaccination. The incidence of TB disease was significantly lower in the BCG arm [Hazard ratio of BCG arm (95% confidence interval): 0.64 (0.46-0.89)]. Interpretation & conclusions: Retrospective data analysis of this community-based trial revealed that BCG revaccination in a community offered modest protection against the development of TB disease at the end of 15 years which, however, requires further evaluation.