Comparison of the Immune Response to Three Different Yersinia pestis Vaccines in Guinea Pigs and Langurs

Abstract

Three different Yersinia pestis vaccines were tested for immune response in guinea pigs and in two species of langurs. Since the immunogenicity of the preparations varied with the animal species used, evaluation of vaccine efficacy was obviously of paramount importance. Guinea pigs were less responsive to killed than to live vaccines but reacted to killed vaccine in large doses or in very small doses containing adjuvant. Immunogenic variations between two killed vaccines were demonstrated in this species. Live Saigon E.V. vaccine readily produced solid immunity in guinea pigs but not in the primates in doses determined by their body weight. Thus the 50% protective dose (PD50) in guinea pigs alone does not reliably reflect the immunogenicity of live vaccine. Some diversity in resistance and immune response to plague were discovered in Presbytis monkeys. So far, Presbytis entellus is the ideal species for evaluation of both live and killed plague vaccines. Presbytis cristata may be less suitable in view of its high susceptibility and inferior immune response to the antigens of Y. pestis. The potency of plague vaccines has heretofore