Fig 1. Flowchart of SKI samples stratified according to age and vaccination status.
Fourtyfour percent of all SKI samples were from male (ex-)cases. (1,2)*: first number: number of cases having τ <24 months; second number: number of cases having τ ≥ 24 months. aP1-4: acellular pertussis vaccination doses 1–4; aP5: acellular pertussis preschool booster dose 5; wP1-4: whole cell pertussis vaccination doses 1–4. According to the Dutch National Immunization Program (NIP) pertussis vaccine primary doses 1–4 are given at 2,3,4, and 11 months of age, and the preschool booster dose 5 is given at 4 yrs of age.