A 6-month-old infant born to an HBsAg-positive mother presents for routine immunisation. The child received HBV vaccine at birth (within 24 hours) and HBIG. What is the most appropriate next step in the immunisation schedule?

Explanation

## Management of Infants Born to HBsAg-Positive Mothers **Key Point:** Infants born to HBsAg-positive mothers require an accelerated HBV vaccination schedule with serological confirmation of response. ### Vaccination Schedule for HBsAg-Positive Mother Infants | Timing | Intervention | |--------|---------------| | Birth (within 24 hrs) | HBV vaccine + HBIG (200 IU) | | 6 weeks | 2nd dose HBV vaccine | | 14 weeks | 3rd dose HBV vaccine | | 9 months | Anti-HBs titre check | **High-Yield:** The accelerated schedule (0, 6 weeks, 14 weeks) differs from the routine schedule (0, 6 weeks, 14 weeks for primary series, then booster at 9-12 months). The critical difference is the timing of the 3rd dose and mandatory serological testing. ### Interpretation of Anti-HBs Titre at 9 Months - **Anti-HBs ≥10 mIU/mL:** Adequate response; routine booster at 12-18 months - **Anti-HBs <10 mIU/mL:** Non-responder; revaccination series required **Clinical Pearl:** HBIG provides immediate passive protection while the vaccine generates active immunity. The combination approach reduces vertical transmission risk from ~90% to <5% if the infant responds adequately. **Warning:** Do NOT delay vaccination or use a standard 3-dose schedule without serological confirmation — this increases the risk of chronic HBV infection in the infant.