Assessment of Anti-HBs Antigen in 6- to 9-Year-Old Children Routinely Vaccinated via Vaccination Program in Iran

Objective: To determine persisting antibody levels to hepatitis B virus (HBV) antigen in healthy children, aged 6–9 years, vaccinated at birth. Methods: Blood samples were collected from 374 vaccinated children (178 girls and 196 boys) and 57 unvaccinated children, attending Shiraz Primary School, Shiraz, Iran from September 2002 to April 2003. An HBV surface antibody (anti-HBs) was determined using enzyme-linked immunosorbent assay. Results: The anti-HBs titer was detected in 17% of the 8-year-old children, 7.7% of the 7-year-old children and 46.6% of the 6-year-old children. The decrease was greatest in the 9-year-old children; more than half (54.3%) had a titer of less than 10 IU/ml, indicating a decrease in antibody levels with increasing age/time. Conversely, more than 35% of the 6-year-old children had a titer greater than 150 IU/ml compared with 24, 12 and 7% of children at the age of 7, 8 and 9, respectively, whose antibody titer was less than 150 IU/ml. Conclusion: Antibody titer declined with time. In comparison with other countries, the antibody titer in Iranian children was much lower.