Safety and immunogenicity of an acellular pertussis vaccine in premature infants.

OBJECTIVES To evaluate the safety and immunogenicity of a two-component acellular pertussis vaccine in preterm infants. STUDY DESIGN Fifty preterm infants (25-35 weeks of gestation; mean, 30.8 weeks) and 50 term infants as a control group received a two-component acellular pertussis vaccine irrespective of their biological age and actual weight. Adverse reactions were registered by parents on a diary card and reviewed on each visit. Antibodies against pertussis toxoid (PT) and filamentous hemagglutinin (FHA) were determined with an enzyme-linked immunosorbent assay before the first and after the third vaccination. RESULTS The infants of both groups showed an increase in geometric mean titers (GMT) against PT and FHA after vaccination (3 doses). There was a significant difference of antibody concentration between the preterm and the control group. The GMT for PT antibody of the preterm infants was 64. 16 U/L, and for the term infants it was 98.96 U/L. The GMT for FHA was 50.92 U/L in preterm versus 86.02 U/L in the control group. Efficacy of the immunization (more than a fourfold increase of antibody concentration in each infant) was 93.5% in the preterm group with respect to PT and 82.6% with respect to FHA. The incidence of adverse reactions was low and comparable in both study groups. CONCLUSION Immunization with an acellular pertussis vaccine is safe for preterm infants. The immune response is significantly lower compared with a control group of term infants, but efficacy is high.