Formalinized vaccines prepared from the spherule-endospore phase of Coccidioides immitis (produced in vitro) were superior in mice to vaccines prepared either from the arthrospore or mycelial growth phases. A majority of the mice immunized with spherule-endospore vaccines survived during observation periods up to 6 months after intranasal challenge with arthrospore doses that greatly exceeded those lethal to most of the control mice. Although immunized survivors appeared to be in good health, a high percentage were still infected when autopsied but the mycosis appeared to be nonprogressive.

Postchallenge survival ratios were high in animals vaccinated with 2.0 mg of the spheruleendospore vaccine but were low when the dosage was reduced to 0.4 mg or less. Both spherules and free endospores possessed immunogenic attributes which were associated primarily with a particulate fraction from disrupted organisms, possibly the cell walls.

Immunizing activity also was present in a formalinized vaccine which contained spherules and endospores that developed in mouse lungs. There was indication that the latter vaccine was more effective when administered subcutaneously than intramuscularly although this was not a feature of spherule-endospore vaccines produced in vitro.

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This work was supported by the Bureau of Medicine and Surgery, United States Navy, and the Office of Naval Research, Washington, D. C., under a contract with the Regents of the University of California. Reproduction in whole or in part is permitted for any purpose of the United States Government.

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