The world is close to eliminating polio once and for all.

Just a few decades ago, polio was crippling more than a thousand children each day. Now the paralyzing virus is endemic to only three countries — Afghanistan, Pakistan and Nigeria. And there were just 223 cases globally last year.

There have been setbacks recently, including reports of suspected cases inside Syria and an outbreak in Somalia.

This timeline explores how polio went from one of the most feared illnesses in the world to a disease on the ropes.

During the past few decades, governments, foundations and nonprofits have joined forces to train thousands of health workers, immunize millions of kids and develop stronger vaccination systems that are also reaching children with other health services.

Until the transmission of poliovirus is stopped in endemic countries, the threat of outbreaks in other areas of the world remains. Nevertheless, health leaders are aiming to eradicate polio completely by 2018.

Author and historianDavid Oshinskyis the Director of Medical Humanities at the New York University School of Medicine. He won the 2006 Pulitzer Prize for his bookPolio: An American Story.

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