Kinetics of the immune response to the (F1 + V) vaccine in models of bubonic and pneumonic plague

Protection against aerosol challenge with >300 MLD of Yersinia pestis was observed 7 days after a single immunisation of mice with the F1 + V vaccine. At day 60, mice were protected against injected challenge (107 MLD) in a vaccine dose-related manner. Recall responses to rV in splenocytes ex vivo at day 98 correlated significantly (p < 0.001) with the immunising dose-level of V antigen; no memory response or anti-V serum IgG was detected in killed whole cell vaccine (KWCV) recipients. This may explain the susceptibility of KWCV recipients to aerosol challenge and the enhanced protection conferred by the F1 + V sub-unit vaccine, particularly since the anti-F1 responses induced by either vaccine were similarly IgG1-polarised.