Oropharyngeal Colonization of Haemophilus influenzae Type b and Serologic Response After Administration of Third Dose of Pentavalent Vaccine to 12-Month-Old Children in Karaj, Iran, 2016

The administration of Haemophilus influenzae type b (Hib) conjugate vaccine led to a decrease of over 90% in the prevalence of severe Hib diseases in the countries with universal coverage vaccine. After addition of Hib vaccine to the national vaccination program and since no study has yet investigated this subject. The current study aimed at investigating the serologic response and assessing oropharyngeal colonization with Hib after the last dose of vaccine. A total of 500 blood and oropharyngeal samples were collected from one-year-old children referred to Karaj health care centers, Iran. Demographic information and risk factors of the children were collected. Oropharyngeal and blood samples were transferred to the laboratory to determine antibody titer by the enzyme-linked immunosorbent assay (ELISA) technique, culture testing, and polymerase chain reaction (PCR). In the current study, 11.8% of children (95% confidence interval (CI): 8.97 - 14.63) had an anti-Hib IgG titer of ≥ 5 µg/mL. Geometric mean titer (GMT) of vaccine antibody was 6.92 µg/mL (95% CI: 6.76 - 7.08); 9% of oropharyngeal culture results were positive for H. influaenzae (non-type b) and 8.2% were confirmed by PCR. Prevalence of oropheryngeal Hib colonization was 0.02%. There was no significant correlation between the titer of H. influaenzae antibody and positive culture of H. influaenzae and the other studied variables (P > 0.05). In Iran, similar to most countries, pentavalent vaccine in national vaccination program decreased the prevalence of Hib colonization. Prevalence of Hib colonization is an important factor in invasive diseases incidence. It is suggested that further studies asses the prevalence of invasive Hib diseases after national vaccination.