A Pakistani polio vaccination worker makes cross on a poster during a protest against the killing of their colleagues in Islamabad on December 19, 2012. Gunmen in Pakistan mounted fresh attacks on health workers carrying out polio vaccinations, taking the death toll to nine and prompting UNICEF and WHO to suspend work on a campaign opposed by the Taliban. Pakistan is one of only three countries in the world where polio is still endemic, but efforts to stamp out the crippling disease have been hampered by resistance from the Taliban, who have banned vaccination teams from some areas. AFP PHOTO/Aamir QURESHI (Photo credit should read AAMIR QURESHI/AFP/Getty Images)

A Pakistani polio vaccination worker makes cross on a poster during a protest against the killing of their colleagues in Islamabad on December 19, 2012. Gunmen in Pakistan mounted fresh attacks on health workers carrying out polio vaccinations, taking the death toll to nine and prompting UNICEF and WHO to suspend work on a campaign opposed by the Taliban. Pakistan is one of only three countries in the world where polio is still endemic, but efforts to stamp out the crippling disease have been hampered by resistance from the Taliban, who have banned vaccination teams from some areas. AFP PHOTO/Aamir QURESHI        (Photo credit should read AAMIR QURESHI/AFP/Getty Images)