The cost of epidemiological transition: a study of a decrease in pertussis vaccination coverage

Based on a transfer function intervention model applied to epidemiological data of pertussis incidence and pertussis vaccination in England and Wales, the consequences of pertussis vaccination strategies were estimated in terms of health effects and economic direct costs. It was established that sixth dose pertussis vaccination programs at 90% coverage were the most cost saving for short-term and for long-term vaccination prevention strategies. We considered two alternative strategies with whole-cell or acellular vaccines for primary course and acellular vaccine for two booster doses in children and one booster in adolescents. As a rule, programs based on exclusive use of acellular vaccines for all the doses were more expensive. Direct costs of programs with the vaccination rate at 90% remained systematically lower than the expected cost of pertussis disease in the case of non prevention. The stability over time of the vaccination coverage at a constant level of 90% made it possible to ensure the largest cost saving strategy during the period of 14 years of analysis. Transitions to programs with a lower proportion of vaccinated children systematically incurred an incremental direct cost for society. The amount of that cost rose with the size of the drop in the new vaccination coverage and diminished, due to the J-curve optimistic effect, when the fall in vaccination rate generated a delayed increase in notification cases of pertussis.