**Core Concept**
The Hepatitis B vaccine induces a humoral immune response by stimulating B cells to produce antibodies against the surface antigen (HBsAg) of the Hepatitis B virus. This results in the production of surface antibodies (anti-HBs) that neutralize the virus.

**Why the Correct Answer is Right**
After vaccination, the patient's serum will contain anti-HBs antibodies, which are a result of the immune system's response to the vaccine. These antibodies are crucial for protecting against Hepatitis B infection. The production of anti-HBs antibodies is mediated by B cells and T cells, which recognize the HBsAg antigen and activate an immune response. The presence of anti-HBs antibodies indicates successful immunization against Hepatitis B.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the question, as it does not describe a consequence of Hepatitis B vaccination.
**Option B:** This option is incorrect because it refers to the presence of the Hepatitis B virus itself, rather than the immune response to the vaccine.
**Option C:** This option is incorrect because it describes a different aspect of the immune response, specifically cell-mediated immunity, which is not directly related to the presence of antibodies.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the presence of anti-HBs antibodies indicates immunity to Hepatitis B, but the absence of anti-HBs antibodies does not necessarily indicate susceptibility to the virus. This is because some individuals may have a natural immunity to Hepatitis B due to past exposure or genetic factors.

**Correct Answer: C. Presence of anti-HBs antibodies.**