Dose-response to a two-component acellular pertussis vaccine in infants and comparison with whole-cell vaccine.

In an effort to determine the optimal dose of pertussis toxoid (PT) and filamentous haemagglutinin (FHA) for use in acellular pertussis vaccines we compared the immunogenicity and safety of acellular pertussis vaccine combined with diphtheria and tetanus toxoids containing 12.5 microg (DTaP-12.5) or 25 microg (DTaP-25) each of PT and FHA with a whole cell pertussis vaccine in infants immunized at 2, 4 and 6 months of age. Recipients of acellular vaccines developed higher anti-FHA concentrations and more rapid anti-PT serological responses that infants who received whole cell pertussis vaccine combined with diphtheria and tetanus toxoids (DPT). A dose response was noted; infants immunized with DTaP-25 developed significantly (P<0.03) higher anti-FHA and anti-PT levels than infants who received DTaP-12.5. No rise in the agglutinin titres was noted for recipients of the acellular vaccines although this vaccine stimulated increases in agglutinins when given as the fourth or fifth dose to children who had received three doses of DTP. The rates of erythema, induration, pain, irritability, crying, increased sleepiness, and decreased appetite were significantly (P</=0.05) lower in infants who received acellualr vaccines than in infants who received DTP. When the data from the injections at 2, 4 and 6 months of age were combined, no significant differences in the rates of any adverse event were noted for recipients of DTaP-12.5 or DTaP-25. The rates of most adverse reactions following DTP decreased from the first to the third immunization except fever, which increased. For acellular vaccine recipients, the rates of fever and erythema increased somewhat from the first to the third injection but remained far below the rates following DTP. The acellular vaccine was safe and immunogenic, and a dose-response effect was demonstrated.