In 1979, a photographer named Janet Parker got a disease that wasn't supposed to exist anymore. At first she thought she had the flu, but then she kept getting sicker, got a rash, and went to the hospital, where doctors—in disbelief—diagnosed her with smallpox. Just a year earlier, the World Health Organization had declared that "mankind probably had seen its last case of smallpox," according to The New York Times. That should have been true.

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