The duration of BCG-induced tuberculin sensitivity in children, and its irrelevance for revaccination. Results of two 5-year prospective studies.

It had been shown earlier, in a retrospective study, that tuberculin sensitivity is stronger in children tested for the second time after vaccination than in those tested for the first time after vaccination. The hypothesis that the tuberculin test itself may reinforce sensitivity to a further test has now been confirmed in 2 strictly controlled prospective studies, which are reported here. The results refer to the tuberculin reactions 5 years after vaccination. These reactions were significantly larger in children who had had an intermediate test (less than 5 years after vaccination) than in those tested for the first time at 5 years. This was found equally for several BCG products, but there was a significant tendency for the PPD batch RT 19-20-21 to have a more pronounced effect than the other tuberculins.It follows from the results of these studies that a possible waning of tuberculin sensitivity cannot be revealed by regular tuberculin testing. Moreover, experiments in guinea-pigs have shown that restoration of sensitivity by means of an injection of tuberculin does not influence the acquired resistance; there are no particular reasons to believe that this should be different in man. Thus the authors consider the very common practice of giving regular tuberculin tests to vaccinated children, in order to decide on possible revaccination, to be devoid of any scientific basis.