Which effect explains why mRNA COVID-19 vaccines often require a booster dose to provide longer-lasting protection against new variants?

💡 Explanation

Reduced long-term protection occurs because B cell affinity maturation, which leads to higher-affinity antibodies, takes time to develop fully after the initial vaccine exposure. Therefore, booster shots enhance this maturation process, rather than issues with original antigenic sin dominating, innate immunity, or antibody switching.

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