How vaccines work: how a shot trains your immune system
Immune memory: why most people catch measles only once
In 1846, measles came to the Faroe Islands and made most people sick. Some very old people stayed well. They had caught it when they were young, 65 years before. What did their bodies keep all that time?
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Miva just had a baby, and you want to visit them. First, you stop at the town clinic. Rono is the nurse there, and he asks you a strange question about your childhood.
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Your old vaccine record is lost, so you can't tell. Rono says it matters. People who had measles as children almost never catch it again, because their body remembers it.
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A body that remembers an illness for a whole life? A young doctor saw it happen. In 1846, a ship brought measles to the Faroe Islands, far out in the North Atlantic. About three people in four got sick.
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Denmark sent a young doctor, Peter Panum, to help. He went from village to village. He wrote down who got sick, and when.
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Then he noticed something odd. Some very old people did not get sick at all. Each of them had caught measles when they were young, in 1781, the last time it came to the islands.
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Their bodies had beaten measles once, 65 years before, and kept a memory of it all that time. The second time, the body beat the virus so fast that they never felt sick.
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Your body's defences are called the immune system. When it remembers a germ like this, you have immunity to it. The first meeting can make you sick. The next ones usually don't.
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This memory has a price. To get it the natural way, your body must first fight the real germ, and you get sick. Measles can be a dangerous illness, most of all for young children.
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Go further
A word Panum found on the islands.