Primary vaccination and revaccination of young adults with BCG: a study using immunological markers

Questions have been raised about the effectiveness of Bacille Calmette-Guérin (BCG) vaccination against tuberculosis (TB) in adults. We therefore analysed the immune response after BCG vaccination in primary-vaccinated and revaccinated young adults. 31 tuberculin skin test (TST) negative healthy students were BCG-vaccinated; 15 were primary-vaccinated and 16 revaccinated. Tuberculin-induced lymphocyte transformation (LT) and cytokine production of peripheral blood mononuclear cells were studied before BCG vaccination, as well as after 2 months and 1 y. In the primary-vaccinated as well as the revaccinated group the LT response increased after 2 months and remained significantly higher than baseline values after 1 y. In both groups the interferon-gamma (IFN-gamma) levels increased significantly after 2 months and the increase was maintained after 1 y. LT increased more in the revaccinated group than in the primary-vaccinated group, while the increase in IFN-gamma response did not differ between the 2 groups. Both primary vaccination and revaccination of TST negative young adults caused a significant increase in the T-helper 1-type immune response, suggesting a protective effect against TB. The present in vitro results thus support the policy in several low-endemic countries of primary vaccination as well as revaccination of young adults at risk of TB exposure.     

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

SETTING: Revaccination of tuberculin-negative school-children 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%CI 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 tuberculin-positive/non-revaccinated 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.