Study of Serologic Response Rate to Haemophilus influenzae Type B After Administration of the Third Dose of Pentavalent Vaccine in Children Aged 12 Months in Karaj City in 2016

background: hib conjugate vaccine has led to more than 90% decline in the prevalence of severe hib diseases in countries with universal coverage vaccination program. after the addition of hib vaccine to the national vaccination program with 3p (three doses of 2, 4, and 6 months) in ir iran, we decided to study the vaccine efficacy after the last dose of vaccine in iranian children in 2016. methods: 500 blood samples were collected from one-year-old children who referred to the health care centers in karaj. demographic information was gathered by a questionnaire. blood samples were sent to a laboratory for antibody titer determination by elisa method. results: 41.2% of the children (95% ci: 36.89 - 45.51) had a titre of igg against hib (0.15 to 1 µg/ml) (short-term protection) and 57.4% of the children had a titre of igg against hib (95% ci: 53.07 - 61.73) equal to or greater than 1 µg/ml (long-term protection). antibody gmt was 6.92 µg/ml (95% ci: 6.76 - 7.08). there was no significant correlation between the titer of h. influaenza antibody and demographic factors. conclusions: in spite of the acceptable gmt titer, children who had antibody titer of < 1 µg/ml comprised approximately 40% of the study population, showing the necessity of further investigation to assess the need for h.flu booster administration.