Immune response of man to Habu-venom toxoid

Immune response of man to various Habu-venom toxoids with different potencies was investigated. A linear relationship was observed between circulating anti-HRI and the amount of HRI toxoid used for the basic immunization. A highly purified toxoid was 2.5 times more effective in man than partially purified ones, when compared on the basis of the immunizing unit determined in guinea pigs. Out of 265 vaccinees, 202 (76.2%) produced anti-HRI exceeding 1 U/ml after two injections of the mixed toxoid and the rate rose to 96% after the booster immunization, when the preparation contained HR1 toxoid of not less than 9 ImU per dose. The rate fell to 58% and 28.5%, 12 months and 24 months after the last injection, respectively. Although booster immunization was effective to restore the declined antibody production, the level of anti-HR1 after the injection did not exceed that after the basic immunization in the groups primed with partially purified HR1 toxoid. Neither increased number of injection nor changed duration of intervals of successive injections for the basic immunization improved the immune response of man. Booster effect was slightly higher in the groups primed with a highly purified toxoid, but its magnitude was much smaller than that in the case of other kinds of toxoid (e.g. tetanus toxoid). Anti-HR2 was invariably higher than 1 U/ml, being more than 5-10 U/ml in many vaccinees. However, the behavior after the booster injection was similar to that of anti-HR1. Side reaction was not a serious obstacle in continuing immunization. The volunteers amounted to 8,206, but general reactions were rare, if any. However, allergic reactions of the vaccinees should carefully be checked, since repeated booster immunization may be necessary to maintain immunity.