Immunogenicity of a Haemophilus influenzae type b–tetanus conjugate vaccine when administered separately or in combined vaccines for primary immunization in two consecutive national schedules in Turkey

Summary Background In Turkey, the Haemophilus influenzae type b–tetanus toxoid conjugate vaccine (Hib) was replaced by the combined diphtheria–tetanus–acellular pertussis and inactivated polio vaccine (DTaP–IPV/Hib) in 2008. This shift to the new schedule created different cohorts of vaccinated children as a consequence of the different schedules used. We evaluated the immunogenicity of the Hib vaccine in infants vaccinated with these different schedules. Methods Three groups of children were evaluated: group 1 comprised 145 infants vaccinated with diphtheria, tetanus, and whole cell pertussis (DTwP), oral polio vaccine (OPV), and Hib vaccines simultaneously at separate sites; group 2 comprised 204 infants vaccinated with the DTaP–IPV/Hib combined vaccine; group 3 comprised 100 infants vaccinated with a mixed schedule of DTwP, OPV, and Hib for the first one or two doses, followed by DTaP–IPV/Hib vaccine to complete the series. Results Anti-polyribosylribitol phosphate (anti-PRP) titers ≥0.15 μg/ml were similar in groups 1, 2, and 3. However, in group 1, who received all the vaccines at separate sites, ≥ l.0 μg/ml long-lasting antibody titers and anti-PRP geometric mean titers were higher ( p = 0.001). Conclusion This study showed that even one dose administered in combination with other vaccines in a primary series decreased the level of anti-PRP.