Vertically acquired occult hepatitis B virus infection may become overt after several years.

OBJECTIVES: To study the frequency of vertically acquired occult hepatitis B virus (HBV) infection (OBI).

METHODS: We investigated 44 children born to hepatitis B surface antigen (HBsAg) positive mothers. They received HBV vaccine directly after birth and at 2, 6 and 52 weeks of age; eight with HBeAg-positive mothers also received hepatitis B immunoglobulin (HBIG). HBV DNA was analyzed in blood collected at 6 weeks and 12 months of age, and HBV antibodies at 12 and 18 months of age.

RESULTS: HBV DNA, but not HBsAg or anti-HBc, was detected at 12 months of age in three children. The viral sequences were almost identical with HBV DNA from their mothers who all were HBeAg-positive and had received tenofovir during pregnancy. Follow-up at 5-7 years age showed that one of the three children had become seropositive for HBsAg and anti-HBc. This child and one of the other two had detectable HBV DNA at the follow-up, with whole genome sequences identical to those in HBV from their mothers.

CONCLUSIONS: Mothers-to-child transmission of HBV can, despite adequate prophylaxis, lead to OBI which may later develop into overt HBV infection. Whether such infections are of clinical importance needs to be further investigated.