Thanks to the longstanding, widespread and effective use of vaccines, the United States hasn't had a reported case of polio in 35 years. The dreadful disease has been nearly wiped off the face of the Earth since then, but the threat isn't over, at least not yet.The virus remains active in small pockets of Pakistan, Cameroon and Syria and a few neighboring countries, and until polio is eradicated worldwide, any country is just a visit away by an infected person from having polio potentially re-introduced within its borders.
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