Efficacy of the BCG revaccination programme in a cohort given BCG vaccination at birth in Hong Kong

SETTING: Revaccination of tuberculin-negative schoolchildren is a regular practice in Hong Kong. OBJECTIVE: To assess the efficacy of BCG revaccination guided by tuberculin skin testing. METHOD: A cohort of 303 692 children vaccinated at birth was followed through the tuberculosis notification register for the development of active disease. The percentage of cohort who participated in the BCG revaccination program during primary school was estimated from the vaccination statistics of the Hong Kong Department of Health. The BCG revaccination history of identified cases was ascertained through vaccination cards and clinic records. RESULTS: A total of 85.2% of the cohort participated in the BCG revaccination programme; 79.7% of the participants were tuberculin-negative and revaccinated; 343 developed tuberculosis after the age of 11; 302 were among the participants in the programme while 41 were not. The tuberculosis incidence was 16.5 and 12.9 per 100 000 person-years for participants and non-participants, respectively (RR 1.28, 95% Cl 0.92-1.77). Among the participants, tuberculosis incidence was 12.5 and 32.0/100 000 person-years, respectively, for the tuberculin-negative/BCG revaccinated group and the tubercuhn-positive/nonrevaccinated group (RR 0.39, 95% CI 0.31-0.49). CONCLUSION: This study failed to demonstrate any significant difference in the incidence rates of tuberculosis among participants and non-participants in a school BCG revaccination programme. The increased risk for tuberculosis in the tuberculin-positive group does not support the use of the tuberculin testing for detection of immunity conferred by neonatal BCG vaccination.