STANDARDIZATION AND CONTROL OF TOXOID COMPONENTS IN THE COMBINED VACCINE (DPT)

Abstract
A previous paper (Yamamoto et al., 1972) stated that the potency of tetanus toxoid in the combined vaccine (DPT [diphtheria, pertussis, tetanus]) varied greatly when assayed against the current National Standard Tetanus Toxoid (plain, NSTT) and that the latter might not be suitable as the reference for the assay of the toxoid component in combined vaccines. Since the fact seemed to raise a serious problem about the validity of the current assay method (called MR64 method), another experiment was conducted to confirm the previous finding by using NSTT and 2 combined vaccines, DPT 368 and DPT 168/268P. The first 2 were used in the previous experiment. The last one was a freeze-dried combined vaccine deprived of pertussis cells by centrifugation and containing 20% normal guinea pig serum to facilitate freeze-drying. On reconstitution with saline, the sample contained 50 Lf [Limes flocculation units] and 9 Lf of diphtheria and tetanus toxoids, respectively. These results show clearly the inadequacy of the MR64 method for the potency test of tetanus toxoid in combined vaccine. The fact may explain why discrepancies were often observed in duplicate tests by National Institute of Health (NIH) [USA] and manufacturers in Japan (Yamamoto et al., 1972).