Objective. To evaluate within the first 6 months of birth the immunogenicity of a 3-component acellular pertussis (aP) vaccine containing filamentous hemagglutinin (FHA), pertactine (PRN), and genetically detoxified pertussis toxin (PT) in infants who received a dose of vaccine at birth, in addition to the recommended schedule administered at 3, 5, and 11 months. Furthermore, we investigated the influence of maternal antibodies on aP vaccine response.

Methods. We used enzyme-linked immunosorbent assay to evaluate immunoglobulin G antibody levels in 45 infants immunized at birth and at 3, 5, and 11 months (group 1) and in 46 infants immunized at the ages of 3, 5, and 11 months (group 2). All mothers were also tested at delivery.

Results. At the age of 5 months the geometric mean titer of anti-PT, anti-FHA, and anti-PRN was significantly greater in group 1 (who had received 2 doses) than in group 2 (1 dose). At 6 months geometric mean titers were significantly higher in group 1 than in group 2 for anti-PRN and anti-FHA, whereas no significant differences were observed for anti-PT.

Conclusions. Immunization at birth may be important for an earlier prevention of the pertussis disease in infants under 6 months, especially in Italy, where the recommended ages for aP vaccine administration are 3, 5, and 11 months.

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