Why does vaccine efficacy often increase after multiple doses, even with the same antigen?

💡 Explanation

Vaccine efficacy increases with multiple doses because of increased B cell affinity maturation. Repeated antigen exposure drives somatic hypermutation and selection of B cells with higher affinity antibodies. Therefore, the immune response becomes stronger and more targeted, rather than relying on initial, lower-affinity antibodies or other immune modulation mechanisms.

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