Why conjugate vaccines work in infants
Pure polysaccharide vaccines produce weak, short-lived responses in infants. Attaching the polysaccharide to a protein carrier improves the response because:
Answer A: explanation for every choice
A
Correct. Polysaccharides alone are T-independent antigens. Linking them to a protein lets B cells present carrier peptides on MHC II to helper T cells, which drive class switching and memory.
B
T-cell help, not innate recognition, explains the durable response.
C
Infants don't already have antibodies to the carrier that explain this effect.
D
Peptides from the carrier are presented on MHC II to CD4+ T cells, not on MHC I.
TakeawayConjugate vaccines turn T-independent antigens into T-dependent ones.
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Reviewed 2026-11-05 by a medical student. Spot an error? Report it with question ID bb182.