In the last 20 years, the number of polio cases around the world has dropped by 99%. The UN World Health Organization reports that the disease remains endemic in only four countries: Afghanistan, Nigeria, India and Pakistan. Of those, Afghanistan and Pakistan are closest to eradicating the disease.

In a final push against polio, health workers in Pakistan have recently started going door to door to give out free polio vaccinations. But those field workers are encountering resistance, as Will Everett reports from Peshawar, the capital of the Northwest Frontier Province.

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