**Core Concept**
Polysaccharide vaccines are composed of the sugar (polysaccharide) component of the bacterial cell wall, which elicits a humoral immune response without the need for adjuvants. These vaccines are effective in providing herd immunity and are often used in individuals with weakened immune systems.

**Why the Correct Answer is Right**
The Meningococcal polysaccharide vaccine is made from the capsular polysaccharide of Neisseria meningitidis, which is responsible for causing meningococcal disease. The vaccine elicits an immune response against the polysaccharide capsule, which is essential for the pathogenicity of the bacteria. This type of vaccine is effective in preventing invasive meningococcal disease and is often used in outbreaks or for individuals at high risk.

**Why Each Wrong Option is Incorrect**
**Option A:** Pertussis vaccine is a toxoid vaccine, which is made from inactivated toxins produced by Bordetella pertussis. It does not contain polysaccharide components.
**Option B:** Hepatitis B vaccine is a recombinant DNA vaccine, which is made by using genetic engineering to produce HBsAg (hepatitis B surface antigen) in yeast cells. It does not contain polysaccharide components.
**Option D:** Yellow fever vaccine is a live, attenuated vaccine, which is made from a weakened form of the yellow fever virus. It does not contain polysaccharide components.

**Clinical Pearl / High-Yield Fact**
Polysaccharide vaccines are often used in individuals with weakened immune systems, such as those with HIV/AIDS or undergoing chemotherapy, because they do not require adjuvants and are less likely to cause adverse reactions.

**✓ Correct Answer: C. Meningococcal. Meningococcal polysaccharide vaccine**