Editor,—There is no doubt that BCG increases sensitivity to tuberculin but this cannot be taken to equate with protection against tuberculosis as is implied by a number of studies including 2 cited in the article by Bannon.1 Evidence from the large Medical Research Council (MRC) trial in the UK showed that after BCG vaccination, non-responders to a 3 tuberculin unit (TU) Mantoux test had the same degree of protection against tuberculosis as responders.2 The delayed hypersensitivity reaction should not be regarded as evidence of immunity but as evidence of infection. Distinguishing a BCG infection from tuberculosis infection may be difficult and the tuberculin test is …