Which of the following vaccines is a polysaccharide vaccine?

The meningococcal vaccine is classified as a polysaccharide vaccine because it is derived from the polysaccharide capsules of the Neisseria meningitidis bacteria. These capsules are made up of chains of sugar molecules and play a key role in the bacteria's ability to evade the host's immune system. Polysaccharide vaccines work by stimulating an immune response that facilitates the production of antibodies against the specific polysaccharides, providing protection against the infections caused by these encapsulated bacteria.

In contrast, the BCG vaccine is a live attenuated vaccine used for tuberculosis; the Hib vaccine, which protects against Haemophilus influenzae type b bacteria, is a conjugate vaccine rather than a polysaccharide one, incorporating a polysaccharide attached to a protein to enhance the immune response; and the influenza vaccine is typically an inactivated or live attenuated vaccine using virus components, not polysaccharides. The distinction of polysaccharide vaccines is important in understanding how different vaccines function and their implications in immunization strategies.