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Plague immunization. I. Past and present trends.

Due to the erroneous concept relating reactogenicity to immunogenicity, killed plague vaccines were initially produced and standardized to insure that the majority of persons receiving them would experience severe local and systemic reactions. Subsequent studies have resulted in the production of relatively nontoxic, killed plague vaccines. Throughout the world the use of highly immunogenic, living, attenuated plague vaccines has resulted in frequent adverse local and systemic reactions. Modification of the route of administration of these vaccines has not substantially altered either the frequency or the severity of adverse reactions. The evidence presented in the literature indicates that programs of mass immunization with highly immunogenic, living, attenuated strains of Yersinia pestis are accompanied by harmful side effects.