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The virus, transmitted by mouth or through feces, reproduces in the blood and then invades the nervous system. At its worst, it attacks the anterior horn cells, which tell the muscles what to do.
Killing those cells is like “cutting the wire to a lamp,” said Walter A. Orenstein, an associate director at the Emory Vaccine Center focused on polio eradication. “The electricity is out and the muscle becomes flaccid. You can’t use it.”











