Genetic evolution under vaccine pressure: the Bordetella pertussis model.

: A possible genetic selective pressure related to the long-term use of vaccines has been the object of recent theoretical thought and publications. For more than thirty years, an effective vaccine has been in use against whooping cough on a wide scale basis in several countries. Thus, the Bordetella pertussis model may contribute to the analysis of an evolutionary risk linked to the vaccine. To maintain and improve the control of whooping cough, better vaccination coverage must be achieved in countries where prevalence is low. In countries where high vaccination coverage has been achieved over a long period, a trend toward the resurgence of the disease has been observed. Efforts are therefore now being directed toward primary vaccination and boosters. These two targets require new vaccines with fewer side effects. Outbreaks in highly vaccinated populations have been reported, raising the issues of vaccine efficacy, of the long-term effect of vaccines on the transmission of the disease, and of genetic selective pressure. Time trend modifications of circulating strains related to vaccination practices and vaccine types have been observed and are compatible with a selective pressure of the vaccine on related pathogens. However, evidence for a causal relation is lacking. In order to monitor and understand the various effects the vaccine may be having on the effectiveness of immunisation against whooping cough, further surveillance is needed, integrating a standardised characterisation of circulating strains and vaccines by way of a space-time sampling model.