A comparison of the rabbit scarification technique with titrations in cell cultures for the potency assay of smallpox vaccine.

Effective tissue culture methods have been developed for the titration of smallpox vaccines, and it seemed appropriate to study their application as methods for assaying the potency of commercial smallpox vaccines. Thirty-four commercial smallpox vaccines were assayed for potency by titration in both rabbit and monkey kidney cell test systems and by the traditional rabbit scarification method.Approximately 85% of the vaccines showed acceptable potency by the rabbit scarification method. Comparative studies between all three test systems showed that consistent results could be obtained with 79% of all vaccines tested. A similar degree of correlation with the same vaccines was shown by a direct comparison of infectivity titres between the two animal tissue cell systems.Certain discrepancies in the potency of individual vaccines and difficulties inherent in cell culture assay were noted. In view of these deficiencies, it was concluded that further comparison of the rabbit scarification and cell culture methods with vaccines of borderline potency should be studied, and that, until the properties of smallpox vaccines have been compared in the rabbit test, cell culture and man, the cell culture methods should be neither accepted nor rejected.