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Biology

The Immune System's Adaptive and Innate Responses

Quick fact

The innate immune system responds within minutes to hours, but the adaptive system takes days to activate initially; yet on re-exposure, the adaptive response is so fast and strong that you often never notice the pathogen.

Why this is interesting

You're sick, but not really—why do you never catch the same flu twice? The answer lies in a remarkable two-part defense system that includes a rapid response team and a viral memory bank.