**Core Concept**
The pneumococcal vaccine is a type of conjugate vaccine designed to protect against Streptococcus pneumoniae infections, which can cause pneumonia, meningitis, and septicemia. The vaccine targets the polysaccharide capsule of the bacteria, which is responsible for its virulence.

**Why the Correct Answer is Right**
Pneumococcal vaccines are prepared from the capsular polysaccharides of Streptococcus pneumoniae. These polysaccharides are extracted from the bacteria and then conjugated to a protein carrier, such as diphtheria toxin or CRM197, to enhance immunogenicity. This conjugation process allows the immune system to recognize the polysaccharide as a foreign substance and mount a targeted immune response. The polysaccharide capsule of S. pneumoniae is the key virulence factor, and targeting it with the vaccine is crucial for preventing infections.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because pneumococcal vaccines are not prepared from the bacterial cell wall.
**Option B:** This option is incorrect because pneumococcal vaccines do not contain live or attenuated bacteria.
**Option C:** This option is incorrect because pneumococcal vaccines are not prepared from the bacterial DNA.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that pneumococcal vaccines are designed to target the polysaccharide capsule of Streptococcus pneumoniae, which is responsible for its virulence. This is why conjugating the polysaccharide to a protein carrier is crucial for enhancing immunogenicity.

**Correct Answer: C. Pneumococcal vaccines are prepared from the capsular polysaccharides of Streptococcus pneumoniae.**