Breakthrough HBV infection in a vaccinated child due to vaccine escape mutant

Abstract

We present a case of hepatitis B virus (HBV) infection in a boy who had appropriate immunoprophylaxis starting at birth and an apparent protective immune response post-vaccination. His mother and elder sister were HBeAg-positive carriers with a high viral load. He received HB immunoglobulin at birth and HB vaccines at birth, 1, and 6 months. His HBs antigen was negative and anti-HBs was 333.8 mIU/ml at 1 year old. Then, at 2 years old, his HBs antigen became positive at 0.25 IU/ml, but anti-HBs was 115.6 mIU/ml. By direct sequenc-ing gene analysis, G145R mutation and P120Q mutation, which are known as vaccine escape mutations, were found in HBV derived from him, his mother, and his sister. It was considered that the HBV had been transmit-ted horizontally from his mother or sister to him due to immune escape after 1 year of age. For children born to HBV carrier mothers with a high viral load, continuous follow-up after 2 years of age and aggressive booster vaccinations should be considered.