Hepatitis B virus (HBV) is a severe public health problem in Iran. This study was conducted to investigate the intrafamilial transmission of HBV in vaccinated children whose one or both parents were positive for hepatitis B surface antigen (HBsAg).

In a study with retrospective cohort design, 110 exposed cases with HBsAg-positive parent(s) were compared with 110 unexposed controls of the same sex and age groups. The participants were directly asked about demographic characteristics, medical history, and vaccinations. Blood samples were collected and analyzed for HBV infection markers using the ELIZA method.

Overall, 1.8% HBsAg (P = 0.15) and 13.6% hepatitis B core antibody (HBcAb) (P < 0.0001) positivity rates were detected in the exposed group. The hepatitis B surface antibody titer (HBsAb) showed that 34.5% of cases and 56.3% of controls had HBsAb levels > 10 IU/L. There was a significant difference in the protective HBsAb level between the two groups (P < 0.0001). There were significant associations between HBsAb level and gender in the exposed group and decreased HBsAb levels and age.

The high rate of positive HBcAb and HBsAg and decreasing HBsAb levels with age in this study indicate that routine childhood vaccination programs are inadequate in preventing HBV transmission and vaccine routes changing or further booster vaccination is essential. Effective case finding in vaccinated children with HBsAg-positive parents, intradermal vaccination, and hepatitis B immunoglobulin in newborns with HBsAg-positive fathers are suggested.