The problems with polio: toward eradication.

The global health effort to eradicate poliomyelitis (polio) has encountered a number of unforeseen and unpredictable challenges. This article provides a timely review of progress made toward eradication, including the polio vaccines in use, and explores the reasons for delays in eradication target dates. It provides an overview of some of the remaining barriers to eradication and looks toward overcoming these through the Polio Eradication and Endgame Strategic Plan.