Breaking the Last Chains of Poliovirus Transmission: Progress and Challenges in Global Polio Eradication.

Since the launch of the Global Polio Eradication Initiative (GPEI), paralytic cases associated with wild poliovirus (WPV) have fallen from ∼350,000 in 1988 to 22 in 2017. WPV type 2 (WPV2) was last detected in 1999, WPV3 in 2012, and WPV1 appeared to be localized to Pakistan and Afghanistan in 2017. Through continuous refinement, the GPEI has overcome operational and biological challenges far more complex and daunting than originally envisioned. Operational challenges had led to sustained WPV endemicity in core reservoirs and widespread dissemination to polio-free countries. The biological challenges derive from intrinsic limitations to the oral poliovirus vaccine: ( a) reduced immunogenicity in high-risk settings and ( b) genetic instability, leading to repeated outbreaks of circulating vaccine-derived polioviruses and prolonged infections in individuals with primary immunodeficiencies. As polio eradication enters its multifaceted endgame, the GPEI, with its technical, operational, and social innovations, stands as the preeminent model for control of vaccine-preventable diseases worldwide.