The vast majority of new cases are in Pakistan, a country which an independent monitoring board set up by the WHO has called "a powder keg that could ignite widespread polio transmission."

Dozens of polio workers have been killed over the last two years in Pakistan, where U.S. forces located Osama bin Laden using information gained in part under the guise of polio vaccinations. A Pakistani doctor, Shakil Afridi, is currently jailed for his role in the CIA operation that uncovered the al-Qaida leader's hideout. Afridi was involved in a vaccination ruse that led to bin Laden's death and eroded trust in polio programs among many Pakistanis.