Pertussis transmission models and demographic shifts under evolving vaccination programs

Pertussis, a highly contagious infection of the respiratory tract, was one of the main causes of child morbidity and mortality in developed countries, in the pre-vaccine era. Following the scale-up and roll-out of childhood vaccination programs in the 1940s–1960s, the incidence and severity of pertussis decreased drastically. However, despite high vaccination coverage rates for more than 50 years, pertussis is still a re-emerging disease requiring novel vaccination strategies taking full consideration of ongoing demographic shifts. Here, we developed an age-structured transmission dynamics model which allows progressive waning of natural and vaccine-induced immunity, distinguishes between diagnosed and undiagnosed infections, and incorporates imported cases and seasonal infections from out-of-province travel. We also developed techniques to calculate key demographic characteristics required in our transmission dynamics model with age stratification guided by the surveillance data, as well as existing and potential immunization programs. The model was fitted to and validated by the age-stratified pertussis incidence data in the province of Ontario, Canada, and the simulation based on the validated model shows a case distribution shift from adolescents to infants until 2050, and calls for additional boosting immunizations in the province. The fundamental platforms and modeling techniques in this study are suitable for use to assess any other immunization programs for childhood diseases elsewhere.