Studies on the biological activity of two strains of BCG: influence of production conditions.

Batches of freeze-dried BCG vaccine were produced by using two different substrains--Moscow (SL 374a) and Paris (SL 1173 P2). The biological activity of the vaccines was studied by the following tests: In the laboratory--viability, heat stability, homogeneity, skin reactivity, allergenic potency and immunogenicity in guinea pigs. In the field--local lesions and postvaccination tuberculin sensitivity. All the batches were produced by using the same technique and production methods. The Paris substrain vaccines showed less viability, but higher heat stability and skin reactivity. It is to be noted that when the VKL medium was used (instead of Sauton) the Paris substrain vaccines showed much lower immunogenicity in guinea pigs and, at the same time, much higher skin reactivity. In the field studies the Moscow substrain vaccines showed higher local lesions and tuberculin sensitivity. In other experiments vaccines produced from the same substrain (Moscow) but in different production centers were compared. It was found that the vaccines differed (according to the production methods used) in terms of some laboratory tests (viability, heat stability, homogeneity) but these differences were not associated with significant differences when studied in the field.