Okay, let's tackle this question about the marker for determining the efficacy of Hepatitis B vaccination. First, I need to recall the different serological markers associated with Hepatitis B. The question is asking which one is used to check if the vaccine was effective.

The Hepatitis B vaccine works by stimulating the immune system to produce antibodies against the surface antigen of the virus. So the key here is to identify which antibody indicates a successful immune response. The main markers are HBsAg, anti-HBs, HBcAg, anti-HBc, and HBeAg.

When someone is vaccinated, they should develop anti-HBs antibodies. This is the antibody against the surface antigen (HBsAg). So the presence of anti-HBs in the blood after vaccination indicates that the person has developed immunity. Therefore, the correct answer should be anti-HBs.

Now, looking at the other options. HBsAg is the surface antigen itself, which is present in people who are infected, not vaccinated. Anti-HBc is against the core antigen and indicates past or ongoing infection. HBeAg is the e antigen, which is a marker of high infectivity. Those are not indicators of vaccination success.

The clinical pearl here is that anti-HBs is the antibody you want to see after vaccination. If someone doesn't develop anti-HBs, they might need a booster or revaccination. Also, a quantitative test for anti-HBs levels can be done to assess immunity, especially in high-risk individuals like healthcare workers.

So putting it all together, the correct answer is anti-HBs. The other options are either markers of infection or not related to immunity from vaccination.

**Core Concept**
Hepatitis B vaccination efficacy is assessed by detecting **anti-HBs (antibody to Hepatitis B surface antigen)**, which indicates immune protection against viral infection. This antibody neutralizes the virus and prevents hepatocyte infection.

**Why the Correct Answer is Right**
The Hepatitis B vaccine contains recombinant HBsAg, which stimulates B-lymphocytes to produce **anti-HBs antibodies**. Successful vaccination results in detectable anti-HBs in serum, confirming humoral immunity. Quantitative anti-HBs levels >10 mIU/mL are considered protective. This antibody does not cross-react with other Hepatitis B antigens (e.g., HBcAg, HBeAg).

**Why Each Wrong Option is Incorrect**
**Option A:** HBsAg (Hepatitis B surface antigen) is present in infected individuals, not vaccinated ones. Its presence indicates active infection or vaccine failure.
**Option B:** Anti-HBc (antibody to core antigen) reflects past or chronic infection, not vaccine-induced immunity.
**Option C:** HBeAg (e antigen) signifies high viral replication and infectivity, not immune status.

**Clinical Pearl**
Always test for **anti-HBs** post-vaccination, especially in high-risk groups (e.g., healthcare workers). Non-responders may require a booster or alternative vaccine regimen. Avoid testing for HBsAg or anti-HBc to assess vaccine efficacy.

**Correct Answer: B. Anti-HBs**

✓ Correct Answer: D. Anti HBsAg