[Sliver]

Originally Posted by getbak

Before they had the modern milking machines that are used today, dairy farms employed young women to milk the cows. They were called milk maids.

The first vaccine was developed after it was observed that milk maids who had contracted cowpox from the cattle they milked didn't catch smallpox. The pus from their sores was used to infect others and effectively protected those other people from contracting smallpox as well. The word vaccine comes from the Latin word for a cow, vacca.

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