The polio endgame

In 1988, a year when an estimated 350,000 or more children were paralyzed by polio, the World Health Assembly initiated a global effort to eradicate the infection once and for all. It was an audacious undertaking, given that the virus circulates largely undetected, requires laborious cell-culture techniques to confirm infection, and is tackled with vaccines that provide imperfect protection in the gut. Initially, the number of polio cases and countries with infections fell rapidly, particularly as financing and political support increased in the mid-1990s. The last case of paralytic poliomyelitis caused by the serotype 2 wild poliovirus was detected in 1999. The number of new polio cases caused by the two remaining wild serotypes had decreased by 99% between 1988 and 2005, but progress had stalled and there was a danger of failure when wild polio viruses were reintroduced into large areas of Africa and Asia. By the end of 2009,...