Haemophilus influenzae type b antibodies in vaccinated and non-vaccinated children

Background: Invasive Haemophilus influenzae type b (Hib) infection has a high morbidity among young children, but the burden of disease and rate of Hib are different in different regions. The aim of the present study was to investigate the levels of Hib antibodies and the oropharyngeal Hib prevalence in young children. Methods: One hundred‐fifty nine healthy children aged 19–36 months of age were included in this cross‐sectional study. Anti‐polyribosylribitol phosphate (anti‐PRP) antibody concentrations were measured using commercially available enzyme‐linked immunosorbent assay (ELISA), and serotyping of isolated Hib strains was conducted by slide agglutination with specific antisera. Results: Of the study participants, 57 (35.8%) were fully vaccinated (group 1A); 17 (10.7%) were incompletely vaccinated (group 1B), and 85 (53.5%) were non‐vaccinated (group 2). Geometric mean titer (GMT) of anti‐PRP antibody was 3.8 μg/mL, 2.2 μg/mL and 0.49 μg/mL in group 1A, group 1B and group 2, respectively. While all children in group 1 (n = 74) had seroprotective antibody concentrations (≥0.15 μg /mL), of the children in group 2 (n = 85) 31.8% did not have seroprotective anti‐PRP levels (P