Diphtheria, tetanus and pertussis are three serious infectious diseases caused by bacteria and that can be prevented by vaccination. Diphtheria and tetanus are now under control although sporadic cases still occur in highly vaccinated populations, whereas pertussis is re-emerging in some developed countries despite the high vaccination coverage. In this thesis, we have monitored the population immunity level in Belgium in different age groups and studied the immune responses in the context of pregnancy vaccination strategies against diphtheria, tetanus and pertussis. A pentaplex immunoassay was developed for simultaneous detection of IgG antibodies induced by five vaccine antigens i.e. DT, TT, PT, FHA and Prn. We identified an underprotective antibody level against diphtheria and tetanus and confirmed the circulation of B. pertussis among the Belgian adult population. Tdap vaccination during pregnancy induced sustained humoral and transient cellular response in women to the same extent in pregnant and nonpregnant women. High maternal antibodies were efficiently transferred through the placenta closing the susceptibility gap in infants prior to their first DTaP vaccination. All infants showed good antibody responses to the vaccine albeit minor inhibition by residual maternal antibodies was observed for infant antibodies to PT in terms of quantity and quality. Our results indicated that efforts should be made to improve the vaccination status of the adult population, particularly for diphtheria. They also support the recommendation of pregnancy vaccination strategies. The clinical significance of maternal antibodies interference on infant immune response should be further investigated.
