**Core Concept**
Meningococcal vaccines are designed to protect against *Neisseria meningitidis*, a gram-negative bacterium that causes meningitis and sepsis. These vaccines typically target serogroups A, C, W, and Y, which are responsible for the majority of cases.

**Why the Correct Answer is Right**
The meningococcal conjugate vaccine is a polysaccharide-protein conjugate that enhances immunogenicity and provides long-term immunity. This vaccine is particularly effective against serogroups A, C, W, and Y. The meningococcal polysaccharide vaccine, on the other hand, is less effective and primarily used in outbreak situations. The serogroup B meningococcal (MenB) vaccine is a protein-based vaccine that targets the outer membrane vesicle proteins and the porin protein, providing protection against serogroup B meningococcal disease.

**Why Each Wrong Option is Incorrect**
**Option A:** Meningococcal vaccines are available for serogroups A, C, W, and Y, making this an incorrect option.
**Option B:** Serogroup B meningococcal (MenB) vaccine is indeed available, which is why this option is incorrect.
**Option C:** The meningococcal conjugate vaccine is available for serogroups A, C, W, and Y, making this an incorrect option.

**Clinical Pearl / High-Yield Fact**
It's essential to note that meningococcal vaccines are not 100% effective, and booster doses may be required to maintain immunity.

**Correct Answer: D.**