## **Core Concept**
The question tests the understanding of serological markers following Hepatitis B vaccination. Hepatitis B vaccination leads to the production of specific antibodies against the Hepatitis B surface antigen (HBsAg). The primary serological marker of immunity after vaccination is the presence of antibodies to the Hepatitis B surface antigen (anti-HBs).

## **Why the Correct Answer is Right**
The correct answer, **anti-HBs**, is the antibody produced in response to the Hepatitis B surface antigen, which is part of the Hepatitis B vaccine. The presence of **anti-HBs** indicates immunity to Hepatitis B, either through vaccination or past infection. In the context of vaccination, **anti-HBs** levels are used to assess the response to the vaccine. A successful vaccination response is typically indicated by **anti-HBs** levels ≥10 mIU/mL.

## **Why Each Wrong Option is Incorrect**
- **Option A: HBsAg** - This is incorrect because HBsAg (Hepatitis B surface antigen) is a marker of active Hepatitis B infection, not immunity from vaccination.
- **Option B: anti-HBc** - This is incorrect because anti-HBc (antibody to Hepatitis B core antigen) indicates exposure to Hepatitis B but does not differentiate between acute, chronic, or resolved infection; it is not a marker of vaccination.
- **Option D: HBeAg** - This is incorrect because HBeAg (Hepatitis B e-antigen) is a marker of viral replication and infectivity in Hepatitis B infection, not related to vaccination response.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that after Hepatitis B vaccination, the presence of **anti-HBs** confirms immunity. However, it's crucial to differentiate between **anti-HBs** from vaccination (which appears after vaccination) and from natural infection (which appears alongside **anti-HBc**). Vaccine-induced **anti-HBs** typically wanes over time, but usually remains detectable for many years.

## **Correct Answer:** . **anti-HBs**