Enteroviruses: Polio

Abstract

Poliovirus is an RNA enterovirus that naturally infects only humans. In a small proportion of infected individuals, primarily younger children, it attacks lower CNS and spinal cord motor neurons. Depending on the cord level, it can cause poliomyelitis (polio) with partial or complete paralysis of the corresponding muscles. Until vaccines became available in 1955, paralysis due to epidemic poliovirus infection occurred nearly worldwide. By the early 1970s, immunization programs in developed countries had interrupted endemic wild poliovirus (WPV) circulation, but the threat to children in develo** countries remained severe. Thereafter, immunization programs launched by the World Health Organization (WHO) and the Global Polio Eradication Initiative (GPEI) raised prospects that polio, like smallpox before it, might vanish. Recent decades have witnessed a >99.99% reduction in cases, with 20 million paralytic cases and 500,000 deaths prevented. GPEI is now poised to complete the eradication of WPV: Neither WPV2 nor WPV3 has been detected anywhere for a decade, and WPV1 is confined to parts of Pakistan and Afghanistan. Despite 40 years of success with oral polio vaccine (OPV), recent challenges have included reduced immunogenicity in communities with high transmission levels and large outbreaks associated with circulating vaccine-derived polioviruses (cVDPVs) in areas of low OPV coverage. Since 2016, the GPEI has coordinated a global switch from trivalent to bivalent OPV (OPV1 + OPV3), recommended universal routine immunization with at least one IPV dose, and deployed genetically engineered OPV2 to combat large cVDPV2 outbreaks. The strategic and logistic capacity established by the GPEI Endgame for complete eradication will endure as a legacy for future initiatives to control infectious diseases worldwide.

Olen M. Kew has retired.