Post-booster response after undetected anti-HBS antibody level in an 8-year-old girl with an up-to-date Hepatitis B immunization: a case report

Introduction: Hepatitis B immunization is stated in Indonesia's child immunization policy. It consists of four doses of a combination vaccine containing HBV, following a monovalent birth dose, to provide immunity against the Hepatitis B virus (HBV) infection in childhood. Anti-hepatitis B surface antigen (HBsAg) antibodies (anti-HBs antibodies) as low as 10 IU/L are considered protective. Undetected anti-HBs antibodies after an up-to-date immunization still occur and are worrisome for parents. Booster immunization is an option to achieve a good anamnestic response. Pre-booster anti-HBs antibodies below 2 IU/L predict a poor post-booster response. Case Report: An 8-year-old girl with an up-to-date HBV was taken to the outpatient clinic to assess the need for a booster Hepatitis B immunization. Her parents felt that their daughter frequently had common colds since elementary school, so a general check-up was done abroad. Undetected anti-HBs antibody levels after an up-to-date HBV immunization were found, so her parents wanted to know the meaning of the undetected anti-HBs antibody level and why it happened. She had no complaints at the time of the examination, and there was nothing remarkable from the physical examination. This patient was deemed unprotected against subsequent HBV infection and received a Hepatitis B booster immunization. Despite the undetected anti-HBs antibodies, a good anamnestic response was achieved. Result: A good anamnestic response following a booster immunization was proven by a laboratory examination one month later. Conclusion: Anti-HBs antibody levels < 10 IU/L warrant a booster immunization, regardless of the pre-booster level. It is beneficial to measure the post-booster level to determine the next action. Further research should be done to further explore this topic.