Gunmen on motorbikes shot dead nine health workers who were administering polio vaccinations in two separate attacks in Nigeria’s main northern city of Kano yesterday.Related StoriesAt least 51 killed after bus and truck collide in ZambiaFresh crisis in Tunisia as PM's party turns against him19 charged in Pretoria with plotting Congo coupPolice fire tear gas at slain politician Chokri Belaid's funeralIslamists used hostage payoffs from Nicolas Sarkozy's government to fund Mali raids