Duration of allergy and immunity in BCG-vaccinated guinea pigs. A five-year study.

A five-year study has shown that the tuberculin sensitivity of guinea-pigs seemingly wanes completely after BCG-vaccination over the course of years, but it can be restored by a single injection of tuberculin to the same level as that found in newly vaccinated animals of the same age. In contrast the acquired resistance to tuberculosis in guinea-pigs vaccinated several years previously is of intermediate strength, inferior to that of the newly vaccinated, and is not restored (apparently not influenced at all) by the injection of tuberculin. It is thus not possible to follow the course and eventual waning of resistance by means of repeated tuberculin testing, and the very common practice of timing revaccination of the individual according to the outcome of such testing must therefore be considered to be without scientific basis.