A second encounter with the same pathogen usually passes before you notice, because the memory cells are still there and antibodies come out far sooner. The first encounter is slow: macrophages have to patrol and engulf, B and T cells must be mobilised, and only once the invaders are cleared does memory remain. The second response curve therefore rises far more steeply and far higher than the first. Vaccination takes a shortcut through that same mechanism: it trains B and T cells with a harmless antigen, so the memory arrives without the illness.
A second encounter with the same pathogen usually passes before you notice, because the memory cells are still there and antibodies come out far sooner. The first encounter is slow: macrophages have to patrol and engulf, B and T cells must be mobilised, and only once the invaders are cleared does memory remain. The second response curve therefore rises far more steeply and far higher than the first. Vaccination takes a shortcut through that same mechanism: it trains B and T cells with a harmless antigen, so the memory arrives without the illness.
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