"Polio virus still exists in parts of the world, which means this virus could be introduced accidentally into this country again and we could have an epidemic of polio."
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"You might have to travel to a foreign country, and then you might be exposed to the polio virus."
"Only one of many strains of polio has been eradicated. We believe that new strains are being formed."
"Some children suddenly lose their immunity, and we have no explanation for why this happens."