Eradication of polio has been defined in various ways—as elimination of the occurrence of poliomyelitis even in the absence of human intervention, as extinction of poliovirus, such that the infectious agent no longer exists in nature or in the laboratory, as control of an infection to the point at which transmission of the disease ceased within a specified area, and as reduction of the worldwide incidence of poliomyelitis to zero as a result of deliberate efforts, and requiring no further control measures.