**Core Concept**
Pre-exposure prophylaxis (PrEP) for rabies involves administering a vaccine to individuals who are at high risk of exposure to the rabies virus, such as laboratory workers or veterinarians. The human diploid cell vaccine (HDCV) is a type of inactivated vaccine used for PrEP.

**Why the Correct Answer is Right**
The recommended regimen for HDCV PrEP involves administering 3 doses of vaccine, with the first dose given on the day of exposure and the second and third doses given 7 and 21 days later. This schedule is designed to provide adequate immunity against the rabies virus before exposure occurs. The vaccine stimulates the production of neutralizing antibodies against the virus, which helps to prevent infection.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the recommended regimen for HDCV PrEP involves more than 1 dose of vaccine.
* **Option B:** This option is incorrect because the recommended regimen for HDCV PrEP involves more than 2 doses of vaccine.
* **Option D:** This option is incorrect because the recommended regimen for HDCV PrEP involves fewer doses of vaccine than what is typically recommended for post-exposure prophylaxis.

**Clinical Pearl / High-Yield Fact**
It's essential to note that the HDCV vaccine is highly effective in preventing rabies when administered according to the recommended schedule. Additionally, individuals who have received HDCV PrEP may still require post-exposure prophylaxis if they are bitten or exposed to the rabies virus.

**Correct Answer:** C. 3 doses of vaccine