Immunogenicity of 10-valent pneumococcal nontypeable Haemophilus Influenzae Protein D Conjugate Vaccine when administered as catch-up vaccination to children 7 months to 5 years of age.

Background: We evaluated catch-up vaccination schedules with 10-valent pneumococcal nontypeable Haemophilus influenzae Protein D Conjugate Vaccine (PHiD-CV).

Methods: In this open, controlled study, children stratified into 4 age groups (N = 150 each) were vaccinated with PHiD-CV: (a) <6 months reference group: 3 primary doses with booster at 12 to 15 months, (b) 7 to 11 months: 2 doses and booster at 12 to 15 months, (c) 12 to 23 months: 2 doses, and (d) 2 to 5 years: 1 dose. Serotype-specific pneumococcal responses were measured by 22F-inhibition enzyme-linked immunosorbent assay (ELISA) and opsonophagocytic activity (OPA) assay.

Results: In the 7 to 11 months group postbooster antibody geometric mean concentrations (except for 2 serotypes) and OPA geometric mean titers (GMTs) were in the same ranges or higher relative to postbooster values in the <6 months reference group. Following 2 doses in the 12 to 23 months group, the percentages reaching threshold levels for ELISA (except for serotypes 6B and 23F) and OPA (except for serotype 1) were comparable or higher than <6 months reference postbooster values. Antibody geometric mean concentrations and OPA GMTs, while comparable or higher than reference postprimary values, were for some serotypes lower than reference postbooster values. Following 1 dose in the 2 to 5 years group ELISA responses were lower than the reference group for several serotypes.

Conclusions: A catch-up PHiD-CV schedule of 2 doses and booster for children 7 to 11 months of age was acceptable. For children 12 to 23 months of age, 2 doses seem to provide adequate priming although a booster dose might confer further benefit. Responses following 1 dose in children 2 to 5 years of age suggest that 2 doses may be preferable.