Polio is a highly infectious disease without cure caused by a virus that can cause permanent paralysis in a matter of hours. It has existed as long as human society but became a major public health issue in late Victorian times with major epidemics in Europe and the United States. According to an Egyptian stele, the disease has been around for at least 35 centuries. Polio mainly affects children under the age of five.

“The battle of polio” has seen a 99 per cent reduction since the Global Polio Eradication Initiative began in 1988, when one of the world's most feared diseases was endemic in 125 countries and was paralyzing nearly 1,000 children every day.

Polio could be soon becomes only the second human infectious disease after smallpox to be eradicated. Nigeria has marked polio-free year, raising global eradication hopes, reaching a milestone many experts had thought would elude it as internal conflict hampered the battle against polio.

But fight is far from over. As long as a single child remains infected, children in all countries are at risk of contracting polio. Armed conflict, political instability, violence, hard-to-reach populations, poor infrastructures and porous frontiers continue to pose challenges to eradicating the disease and has made it difficult for health workers to make the rounds necessary to provide full immunization. The virus has now been cornered in just two places: Afghanistan and Pakistan.

In Pakistan, where polio has never been eliminated, the C.I.A.’s decision to send a vaccination team into the Bin Laden compound to gather information and DNA samples hurt the national polio drive. The Taliban have claimed that the polio vaccination drive is a front for espionage or a conspiracy to sterilize Muslims. They attack and kill health workers who conduct door-to-door campaigns, forcing the government to mount massive security operations during major vaccination drives.

Viruses cross borders invisibly and dangerously. In Afghanistan, most of the new cases come from Pakistan and Middle East region has become susceptible to an outbreak of it as Polio re-emerged in war-torn Syria after more than a decade.

The Global efforts to eradicate polio have made impressive progress over the past decade and global health experts still hold out hope for an end to polio worldwide by 2018. But armed conflict and chaos are making it tough for the world to wipe out the virus completely.There is no cure for polio, but it  can be prevented through immunization. As long as a single child remains infected, children in all countries are at risk of contracting polio.

** Part of this project has been produced for THE NEW YORK TIMES and with the support of Rotary International

** Locations: Pakistan, Afghanistan, Nigeria, Lebanon and Kurdistan