Question
A mother was diagnosed with hepatitis B surface antigen (HBsAg) during her early pregnancy. To prevent transmission to the child, she received hepatitis B immunoglobulin injections in her later pregnancy. The child was also vaccinated against hepatitis B at birth to block transmission, and a cesarean section and non-breastfeeding were chosen. However, the child was diagnosed with the same HBsAg at nine months old. She wants to know what happened and how to deal with this situation.