In a previous study we found that monovalent acellular pertussis (aP) vaccine at birth and one month achieves higher IgG antibody (Ab) levels to pertussis toxoid (PT), filamentous hemagglutinin (FHA) and pertactin (PRN) by 8 weeks, with compared to controls. Here we report antibody and cell mediated immune (CMI) responses to 4 years of age.
IgG Ab to PT, FHA and PRN, diphtheria (D), tetanus (T) was measured in the 3 groups (aP vaccine at birth and one month, aP birth only and no aP) at 2 years, and pre and post DTaP-IPV vaccine at 4 years. CMI responses to pertussis vaccine antigens were measured at 2 years. Adverse events following DTaP-IPV were recorded.
52 of 74 subjects (70%) were available for follow up. Overall, 11 (21%) had detectable PT IgG at 2 years, decreasing to 10% pre 4 year old booster compared with 100% at 8 months of age. Post the 4 year booster, pertussis antigen IgG levels were similar, but there was a trend to lower PT IgG levels in birth aP infants (GMC 28.7 EI.U/ml) compared to controls (GMC 53.6 EI.U/ml). Th2 cytokine responses to pertussis antigen stimulation were higher in aP recipients at 2 years. There was no difference in injection site reactions among groups following the DTaP-IPV booster at 4 years old.
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.
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