Effectiveness of a single dose of acellular pertussis vaccine to prevent pertussis in children primed with pertussis whole cell vaccine

We estimated the protection given by one booster dose of acellular pertussi s vaccine (aP) given at 18 months or before school entry to children alread y primed with whole cell vaccine (wP). Case-control studies were conducted in these two age groups. In children who received or were eligible to recei ve their 18 months booster, the risk of pertussis was 1.4 and 3.6 times hig her for those with 4 and 3 wP, respectively, compared to those with 3 wP 1 aP. In 5 and 6 yr old children, the risk of pertussis among the subjects with 5 and 4 wP, was 1.4 and 2.1 times higher respectively than in those wh o received 4 wP + 1 aP. A single dose of aP increased the protection agains t pertussis and this protection was greater than that obtained with a wP bo oster. (C) 2001 Elsevier Science Ltd. All rights reserved.