Evaluation of a killed phase I Coxiella burnetii vaccine in cynomolgus monkeys (Macaca fascicularis).

The protective efficacy of a killed, purified, phase I Coxiella burnetii vaccine was tested in cynomolgus monkeys. Monkeys vaccinated once with 30 micrograms of the antigen were challenged 6 or 12 months later with virulent phase I rickettsiae administered in small-particle aerosols. The vaccine provided only partial protection, since some of the challenged monkeys developed clinical signs of illness. However, the vaccinated animals did not develop pneumonia as determined by radiographic evaluation nor any hematologic or chemical changes except for an increase in fibrinogen. Although rickettsiae were isolated from peripheral blood in vaccinated monkeys, the rickettsemia persisted for only 1-2 days; whereas, organisms were recovered from unvaccinated animals for 6-7 days. All vaccinated animals had circulating microagglutinating antibodies to phase I and phase II antigens 6 and 12 months after vaccination.