What does tuberculin reactivity after bacille Calmette-Guérin vaccination tell us?

The effect of bacille Calmette-Guérin (BCG) vaccination on tuberculin reactivity is briefly reviewed. BCG vaccination will almost invariably result in tuberculin conversion with a positive tuberculin skin test developing 4-8 weeks after vaccination. However, these tuberculin reactions will wane-rapidly in all individuals who receive the vaccine in the neonatal period and more slowly in those who are vaccinated at an older age such as during the primary-school years. Of BCG vaccine recipients whose initial tuberculin skin test is negative, 10%-25% will have a positive tuberculin skin test if they are retested within 1-4 weeks-the so-called "booster phenomenon. " There is no relationship between tuberculin reactivity after BCG vaccination and the protective efficacy of the vaccine against development of active tuberculosis. Therefore, the ideal BCG vaccine would produce a scar at the site of injection to identify individuals who have been vaccinated but would have no effect on tuberculin reactivity.