**Core Concept**
Rabies vaccines are classified into two main types: inactivated whole virus vaccines and cell culture vaccines. Cell culture vaccines are produced by growing the rabies virus in a cell culture medium, which is then inactivated to make it safe for human use.

**Why the Correct Answer is Right**
Cell culture rabies vaccines are given to individuals who are already showing symptoms of rabies, such as hydrophobia, agitation, and aggression. This is because the vaccine is most effective when administered after exposure to the virus, but before the onset of clinical symptoms. The cell culture vaccine is also used in areas where the risk of rabies is high, such as in developing countries where dog bites are common.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the cell culture rabies vaccine is not typically used as a pre-exposure prophylaxis (PrEP) for individuals who are at high risk of exposure to the virus, such as laboratory workers or veterinarians.
**Option B:** This option is incorrect because the rabies vaccine is not typically administered to individuals who are already showing symptoms of rabies. In such cases, post-exposure prophylaxis (PEP) with immunoglobulin and vaccination is given, but the cell culture vaccine is not the primary option.
**Option C:** This option is incorrect because the cell culture rabies vaccine is not typically used as a booster dose for individuals who have previously received the vaccine.

**Clinical Pearl / High-Yield Fact**
It is essential to note that the rabies vaccine is most effective when administered promptly after exposure to the virus. Delayed administration of the vaccine can lead to a lower success rate in preventing the disease.

**Correct Answer:** D