Question

The vaccine against Neisseria meningitidis contains which of the following?

• A. Whole bacteria
• B. Capsular polysaccharide
• C. Somatic 'O' antigen
• D. None of these

Hint:

The serogroup-defining outer layer of the meningococcus is the vaccine antigen.

Answer 1

The Correct Option is B

Step 1: Neisseria meningitidis is an encapsulated diplococcus, and its capsule is both the main virulence factor and the target for vaccination.

Step 2: Purified capsular polysaccharides from serogroups A, C, Y and W-135 form the basis of the polysaccharide meningococcal vaccines that have been in use since the 1970s. A single dose gives good protection in older children and adults, taking about 10 to 14 days to develop, though it works poorly in children under three years.

Step 3: Whole-cell preparations are not the basis of this vaccine, and the somatic 'O' antigen belongs to the lipopolysaccharide of enteric Gram negative rods. So the meningococcal vaccine is built on capsular polysaccharide.\[\boxed{\text{Capsular polysaccharide}}\]