Acellular Pertussis Preschool Booster Vaccination
To the Editors:
De Greeff and colleagues have conducted a very interesting and important study of the effect of a preschool booster at 4 years on pertussis incidences in The Netherlands.1 One of their main findings was a significant reduction of 40% in pertussis among children 0–5 months old. We have previously conducted a Danish study looking at the potential indirect effect of a preschool booster on the youngest children.2 We found that a preschool booster at 4 years with satisfactory uptake would prevent 14–33% of pertussis hospitalizations in the youngest children—a more moderate indirect effect than suggested by the Dutch study.
De Greeff and colleagues references our study as a mathematical model. This is only partly true. Our study is first and foremost a nationwide cohort study of hospitalization risk according to the number and age of other children in the household. Our main findings were that ∼50% of all hospitalizations could be attributed to other children in the household, and although the highest risk was associated with household children of the preschool age, younger children were also risk factors. During the study period no preschool booster was in use in Denmark, and to be able to evaluate the impact of a preschool booster on infant pertussis we had to make assumptions of the transmission efficacy of a booster and the uptake—the only modeling in our study. These parameters determine where in the 14–33% range the reduction will lie, but the range itself has been determined through a traditional cohort study of pertussis epidemiology.
When interpreting the Dutch results, it is important to notice that the researchers did not find a reduction among children aged 6–11 months old and that in this study design the 40% reduction could be at least partly a result of secular trends and consequently cannot be solely attributed to herd immunity.
A 5-year booster was introduced in Denmark in late 2003 and we are currently planning a study similar to the one by De Greeff and colleagues which will make for a very interesting comparison.
Anders Hviid, MSc, DrMed Sci
Statens Serum Institute
1.de Greeff SC, Mooi FR, Schellekens JFP, de Melker HE. Impact of acellular pertussis preschool booster vaccination on disease burden of pertussis in the Netherlands. Pediatr Infect Dis J
© 2008 Lippincott Williams & Wilkins, Inc.
2.Hviid A, Stellfeld M, Wohlfahrt J, Andersen PH, Melbye M. The impact of pre-school booster vaccination of 4-6-year-old children on pertussis in 0-1-year-old children. Vaccine