A Pakistani man wheels Jamshid, an 8-year-old girl with polio, around the outskirts of the capital Islamabad last July. Behrouz Mehri/AFP/Getty Images hide caption

itoggle caption Behrouz Mehri/AFP/Getty Images

An Indian boy receives a polio vaccination from an Indian health worker in Amritsar last year. Narinder Nanu/AFP/Getty Images hide caption

itoggle caption Narinder Nanu/AFP/Getty Images

Microsoft founder Bill Gates, his wife Melinda French Gates and British Prime Minister David Cameron at the World Economic Forum on January 28, 2011, in Davos, Switzerland. Johannes Eisele/AFP/Getty Images hide caption

itoggle caption Johannes Eisele/AFP/Getty Images