Long-term pertussis-specific immune responses to a combined diphtheria, tetanus, tricomponent acellular pertussis and hepatitis B vaccine in pre-term infants.

Immunoglobulin G (IgG) antibody titres against pertussis antigens, Bordetella pertussis-specific proliferation and cytokine production by peripheral blood mononuclear cells (PBMCs) were evaluated at the age of 5-6 years in 13 children who had been pre-term infants with a gestational age (GA) of < or = 31 weeks, 10 who had been pre-term infants with a GA of 32-37 weeks, and 15 who had been term infants with a GA of 38-42 weeks. All of the infants had been immunised with a combined diphtheria, tetanus, tricomponent acellular pertussis and hepatitis B vaccine (DTaP-HBV) at 3, 5, and 11 months of post-natal age. Our results show that the long-term immune responses induced by primary pertussis vaccination in the pre-term infants (especially those with a GA of < or = 31 weeks) were qualitatively and quantitatively lower than those observed in the term infants. In order to maintain an adequate pertussis-specific immune response, in term children a booster at 5-6 years of age may be suggested, whereas in pre-term an earlier booster should be useful.