Effectiveness of experimental whole-cell pertussis vaccines in murine model.

Introduction: Since the 1990s pertussis re-emergence has been observed in many highly immunized countries. Genetic divergence between circulating B. pertussis isolates and vaccine strains has been suggested as one of the reasons responsible for the resurgence of pertussis. This divergence was observed in some studies to affect the effectiveness of pertussis vaccine when tested in murine model. In the study, using the murine intranasal challenge model we evaluated the effectiveness of four experimental wP vaccines, prepared with B. pertussis isolates belonging to different PFGE groups, in the elimination of the bacterial infection induced with mixture of the four B. pertussis isolates.

Methods: The experimental wP vaccines were prepared with clinical isolates belonging to PFGE groups V, IVγ and C, used individually or together. The mixture of four isolates classified to PFGE groups V, IVγ, III and C was used as intranasal mice challenge. The chosen strains represent PFGE groups characteristic for isolates currently circulating in Europe (PFGE groups IV and V), specific for Poland (PFGE group C) and vaccine strains of Polish wP vaccine (PFGE group III). Additionally, to study bacterial fitness, changes in the proportions of four isolates used as the challenge within the course of infection in mice lungs were monitored.

Results and conclusions: All experimental wP vaccines were found to be equally effective in eliminating B. pertussis from mice lungs. Their effectiveness was independent on PFGE group of vaccine strain. The results on bacterial fitness during mixed infections induced in the non-immunized mice found the isolate of PFGE group IVγ dominating among the other isolates used in the mixture belonging to PFGE group III, V, and C. This data might suggest that the isolates belonging to PFGE group IV, so commonly seen in Europe, might be more fitted to explore in conditions of waning immunity.