## Core Concept
The meningococcal vaccine is designed to protect against *Neisseria meningitidis*, a bacterium that can cause severe infections like meningitis and septicemia. The vaccine targets specific serogroups of the bacteria, which are labeled by letters (e.g., A, B, C, W, Y). Different regions and populations may have varying prevalent serogroups.

## Why the Correct Answer is Right
The correct answer, **B. Meningococcal B vaccine: Outer membrane vesicle (OMV) and recombinant proteins**, highlights a critical type of meningococcal vaccine. Meningococcal B vaccines use either outer membrane vesicles (OMV) or recombinant proteins to protect against serogroup B *Neisseria meningitidis*. These vaccines are crucial because serogroup B infections are significant causes of meningitis and septicemia, particularly in infants and young children.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because it does not specify a recognized type of meningococcal vaccine.
- **Option C:** This option might refer to polysaccharide vaccines or conjugate vaccines used for other serogroups (like A, C, W, Y), but it does not accurately describe the specific vaccine for serogroup B.
- **Option D:** This option does not accurately describe any commonly recognized meningococcal vaccine.

## Clinical Pearl / High-Yield Fact
A key point to remember is that **meningococcal vaccines are serogroup-specific**. For example, the MenACWY vaccine (conjugate vaccine) protects against serogroups A, C, W, and Y, while MenB vaccines protect against serogroup B. The choice of vaccine often depends on the epidemiological situation and the individual's risk factors.

## Correct Answer Line
**Correct Answer: B. Meningococcal B vaccine: Outer membrane vesicle (OMV) and recombinant proteins**