Reaching the last one per cent: progress and challenges in global polio eradication.

Since its launch in 1988, the World Health Organization's Global Polio Eradication Initiative has reduced worldwide polio incidence by >99%. The most dramatic progress was achieved up to the year 2000, the original eradication target date, but subsequent years have seen only limited progress in preventing the last 1% of cases. Recent gains in India and Nigeria have been offset by continued endemicity in Pakistan and Afghanistan, and repeated reseeding of wild poliovirus into polio-free areas has led to large outbreaks and re-established transmission. Although wild poliovirus type 2 was eradicated in 1999 and wild poliovirus type 3 may be nearing eradication, the continued emergence of circulating vaccine-derived polioviruses, especially type 2, presents ongoing challenges to stopping all poliovirus transmission.