Impact of acellular pertussis preschool booster vaccination on disease burden of pertussis in The Netherlands.

BACKGROUND: An acellular preschool booster vaccination against pertussis has been included in the National Immunization Programme in The Netherlands, since November 2001. We studied the impact of this preschool booster on the epidemiology of pertussis.
METHODS: We analyzed and compared pertussis cases registered in the national notification system, hospital registry, and death registry between the periods 1998-2001 (without preschool booster) and 2002-2005 (with preschool booster).
RESULTS: In 2002-2005, the incidence of hospitalizations and notifications in 1-4 year olds were 48% and 44%, lower respectively, than in 1998-2001. Similarly, in 5-9 year olds the incidence of hospitalizations and notifications had decreased 32% and 15%, respectively. In 2005, vaccine effectiveness for preschool booster among children born between January 1, 1998 and January 1, 2001--all of whom had been eligible for the booster--was estimated at 79% (95% CI: 71-85). In infants aged 0-6 months, the incidence of hospitalizations per 100,000 population decreased 40%, from 222.5 to 133.6. In contrast, among cohorts aged 10-19, 20-59, and >60 years, the incidence of notifications increased 60%, 44%, and 68%, respectively.
CONCLUSIONS: The preschool booster strongly decreased the disease burden in the targeted cohorts. Importantly, the incidence in infants 0-6 months also showed a decline after introduction of the preschool booster, suggesting reduced transmission from siblings to young infants. Meanwhile, the number of pertussis cases in adolescents and adults increased. With prevention of severe pertussis among infants as focus, this effect should not be ignored in the discussion on future vaccination strategies for pertussis.