A 5-year-old boy is detected to be HBsAg positive on two separate occasions during a screening program for hepatitis B. He is otherwise asymptomatiC. Child was given three doses of recombinant hepatitis B vaccine at the age of 1 year. His mother was treated for chronic hepatitis B infection around the same time. The next relevant step for further investigating the child would be to:

**Core Concept**
The child's positive HBsAg status despite vaccination suggests a possible vertical transmission from the mother or vaccine failure. **Hepatitis B virus (HBV)** infection can be acute or chronic, with the latter often resulting from vertical transmission or early childhood infection.

**Why the Correct Answer is Right**
Since the child was vaccinated and still tested positive, it's crucial to determine if the infection is due to vaccine failure or if the child was already infected at birth, making the vaccination ineffective. Further investigation, such as testing for **HBV DNA** or **HBeAg**, can help understand the infection's nature and the child's immune response.

**Why Each Wrong Option is Incorrect**
**Option A:** This choice is not provided, so we cannot assess its accuracy.
**Option B:** Similarly, without the option details, we cannot comment on its correctness.
**Option C:** And this option is also missing.
**Option D:** This option is not available for evaluation.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that **hepatitis B vaccination** does not guarantee 100% protection, especially if the child was infected before or at birth. Regular screening and monitoring, especially in high-risk groups like children of chronically infected mothers, are crucial.

**Correct Answer:** D. Perform a HBV DNA or HBeAg test to confirm the diagnosis and to assess the viral load and infectivity.

✓ Correct Answer: B. Obtain anti-Hbs levels