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.

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 ≥0.15μg/ml were similar in groups 1, 2, and 3. However, in group 1, who received all the vaccines at separate sites, ≥ l.0μg/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.