Pneumococcal polysaccharide vaccine (PPSV23) is immunologically inferior to PCV13 (13-valent conjugate vaccine) in children under 2 years. The reason is:
- A PCV13 contains fewer serotypes and is less immunogenic
- B Polysaccharide vaccines stimulate CD8+ T cells preferentially
- C Polysaccharides are T-independent antigens eliciting predominantly IgM without memory cells in immature immune systems ✓
- D PPSV23 is a live vaccine that cannot be given to infants
Correct answer: C. Polysaccharides are T-independent antigens eliciting predominantly IgM without memory cells in immature immune systems
Explanation
Pure polysaccharide antigens are T-independent type 2 (TI-2) antigens that stimulate B cells directly without T-cell help, producing predominantly IgM (minimal class switching to IgG) with no memory B-cell generation; children under 2 years lack mature marginal zone B cells needed for this response. Conjugate vaccines link polysaccharide to carrier proteins (T-dependent antigen), enabling T-helper cell involvement, IgG class switching, affinity maturation, and memory formation. Neither vaccine is live.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.