Antibody and cell-mediated immunity to pertussis 4 years after monovalent acellular pertussis vaccine at birth

Background: In a previous study, we found that monovalent acellular pertussis (aP) vaccine at birth and 1 month achieves higher IgG antibody (Ab) levels to pertussis toxoid (PT), filamentous hemagglutinin (FHA) and pertactin by 8 weeks, when compared with controls. Here, we report antibody and cell-mediated immune responses to 4 years of age. Methods: IgG Ab to PT, filamentous hemagglutinin and pertactin, diphtheria (D) and tetanus (T) was measured in the 3 groups (aP vaccine at birth and 1 month, aP birth only and no aP) at 2 years of age and before and after DTaP-inactivated polio vaccine (DTaP-IPV) at 4 years of age. Cell-mediated immune responses to pertussis vaccine antigens were measured at 2 years of age. Adverse events following DTaP-IPV were recorded. Results: Of 74 subjects, 52 (70%) were available for follow up. Overall, 11 (21%) had detectable PT IgG at 2 years, decreasing to 10% before 4-year-old booster compared with 100% at 8 months of age. After the 4-year booster, pertussis antigen IgG levels were similar, but there was a trend to lower PT IgG levels in birth aP infants (geometric mean concentrations: 28.7 EI.U/mL) compared with controls (geometric mean concentrations: 53.6 EI.U/mL). The cytokine responses to pertussis antigen stimulation were higher in aP recipients at 2 years of age. There was no difference in injection site reactions among groups following the DTaP-IPV booster at 4 years of age. Conclusions: In the longest reported follow-up of infants who received aP vaccine at birth, we found a trend to lower PT IgG antibodies post booster compared with receipt of first dose of aP-containing vaccine at 8 weeks of age. Short- and long-term antibody responses with and without prior maternal pertussis vaccination are crucial for further evaluation of this strategy for preventing severe early pertussis.Nicholas Wood, Helen Marshall, Olivia J. White, Patrick G. Holt, and Peter McIntyr