A COMPARISON OF PLAGUE VACCINE, USP AND EV76 VACCINE-INDUCED PROTECTION AGAINST YERSINIA-PESTIS IN A MURINE MODEL

The median lethal dose (MLD) of a pathogenic strain of Yersinia pestis was established by three routes of administration in three strains of mouse. There was no significant difference between the MLDs in the di fferent strains of mouse. The MLD by the subcutaneous route in Balb/C and an outbred line was approximately I c.f.u., the MLD following intr aperitoneal administration was tenfold higher. There were significant differences in the mean times to death after administration of the cha llenge by different routes. The relative efficacy of a live attenuated vaccine strain of Y. pestis (EV76),was compared with that of the form aldehyde-killed vaccine (Plague vaccine, USP). EV76 protected against high challenge doses (up to 5.75 x 10(6) MLD), though immunized animal s showed side effects of varying severity. The killed vaccine was less effective in terms of dose-protection (deaths occurred after challeng e with 4000 MLD) and several of the vaccinated animals suffered sub-le thal, plague-related sequelae to the challenge.