## **Core Concept**
The presence of specific hepatitis B virus (HBV) markers in a patient's serum can indicate different stages of HBV infection or immunity. **HBsAg (Hepatitis B surface antigen)** is a marker of current HBV infection, while **anti-HBs (antibody to Hepatitis B surface antigen)** indicates immunity, either from vaccination or past infection.

## **Why the Correct Answer is Right**
When a patient is **anti-HBs positive** but **HBsAg negative**, and all other HBV markers (such as HBeAg, anti-HBe, anti-HBc) are negative, it suggests that the patient has **immunity to HBV**. This can occur in two scenarios: either the patient has been vaccinated against HBV, or the patient had a past HBV infection and has cleared the virus. However, the absence of **anti-HBc (antibody to Hepatitis B core antigen)**, which typically appears during and persists after acute HBV infection, helps differentiate between these scenarios. The presence of **anti-HBs** without **anti-HBc** is most indicative of **vaccination-induced immunity**, as natural infection usually results in both **anti-HBs** and **anti-HBc** being positive.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Incorrect because it does not accurately reflect the scenario described.
- **Option B:** Incorrect because immunity from past infection would typically result in **anti-HBc** being positive.
- **Option C:** Incorrect as it inaccurately describes the scenario or the implications of the markers.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that **anti-HBs** levels should be checked after vaccination to ensure an adequate response, particularly in high-risk individuals. A level of ≥10 mIU/mL is generally considered protective. This scenario highlights the importance of understanding HBV serology in managing patients and assessing their immune status against HBV.

## **Correct Answer:** . Immunity due to vaccination.