Which of the following are examples of pure polysaccharide vaccines?

• A. Varicella
• B. Measles, Mumps, Rubella
• C. Pneumococcal, Meningococcal, Salmonella Typhi Vi
• D. Yellow Fever

Answer: (C)

Pure polysaccharide vaccines use only the polysaccharide capsule antigens from bacteria, without a protein carrier. They stimulate a T-independent antibody response (primarily IgM) and are often less immunogenic in young children, typically needing boosters and not producing strong long-term memory. The examples that fit this category are the pneumococcal polysaccharide vaccine, the meningococcal polysaccharide vaccine, and the Salmonella Typhi Vi polysaccharide vaccine. Varicella and MMR are live attenuated vaccines, and yellow fever is also a live attenuated vaccine, not polysaccharide. Note that some pneumococcal vaccines are conjugate vaccines (polysaccharide linked to a protein) and are not pure polysaccharide vaccines.