Reactogenicity and immunogenicity at preschool age of a booster dose of two three-component diphtheria-tetanus-acellular pertussis vaccines in children primed in infancy with acellular vaccines

Objectives. To determine the reactogenicity and immunogenicity of a fourth dose of 2 three-component acellular pertussis vaccines combined with diphth eria-tetanus-acellular pertussis (DTaP) when administered at preschool age to children primed in infancy with 3 doses of the same DTaP and who had rec eived a diphtheria-tetanus (DT) dose at the age of 12 months. Setting. Local health units of 4 Italian regions. Study Design. Three thousand five hundred twenty-two children, who had been randomized in the first year of life to be immunized with a DTaP vaccine b y either SmithKline Beecham or Chiron Biocine, were offered a booster of th e same vaccine or, if refusing, a DT vaccine at the age of 5 to 6 years. Fa milies of children were aware of the vaccine administered. The occurrence o f adverse events was compared between the children who received a DTaP boos ter and those boosted with a DT only. Antibody titers to pertussis vaccine components (pertussis toxin, filamentous hemoagglutinin, and pertactin) wer e determined on 558 paired sera taken before and 30 days after the DTaP boo ster administration. Results. Four episodes of temperature greater than or equal to 39.5 degrees C, 2 in each DTaP group, were recorded. Fever greater than or equal to 38 d egreesC occurred infrequently in both DTaP and DT recipients (DTaP range: 2 .5%-2.8%; DT range: 0%-4.8%), as did irritability (DTaP range: 10.1%-11.7%; DT range: 7.4%-12.6%). The frequency of local reactions was significantly higher for DTaP recipients (range: 44.0%-52.8%), with respect to DT recipie nts (range: 29.5%-44.4%). Extensive local reactions were observed in 1.2% o f DTaP recipients and in .5% of DT recipients. Both DTaP vaccines induced h igh antibody titers against pertussis toxin, filamentous hemoagglutinin, an d pertactin, with an increase of >10 times the prebooster geometric mean ti ters. Conclusions. A booster dose of DTaP at preschool age in children primed wit h the same acellular pertussis vaccine is safe and immunogenic. However, th e frequency of local reactions is higher compared with that following prima ry immunization and with that following booster with DT only, and parents s hould be informed of the potential for these reactions to occur.