Image copyright AFP Image caption Nigeria is one of only three countries where polio is still endemic 
 
 Nine female polio vaccinators have been killed in two shootings at health centres in northern Nigeria, police have told the BBC. No one claimed responsibility but Islamist militant group Boko Haram, a sect which has condemned the use of Western medicine, has been blamed for carrying out a spate of assaults on security forces in the city in recent weeks. Polio Polio is an infectious disease caused by a virus which invades the nervous system and may cause irreversible paralysis 
 
 It can strike at any age but mainly affects children under five 
 
 There is no cure for polio, it can only be prevented 
 
 Polio vaccine, given multiple times, can protect a child for life. In the past month, polio workers have also been targeted and killed in Pakistan, where the Taliban have threatened anti-polio efforts - accusing health workers of working as US spies and alleging that the vaccine makes children sterile. As long as a single child remains infected with polio, unvaccinated children in all countries are at risk Nigeria's battle to contain polio Bill Gates: The world can defeat polio 
 
 Kano banned motorbikes from carrying passengers after a recent attack on the prominent Muslim leader, the emir of Kano. In 2003, northern Nigeria's Muslim leaders opposed polio vaccinations, saying they could cause infertility and AIDS. As a result of vaccination, it is now only endemic in three countries - Afghanistan, Nigeria and Pakistan. According to the Global Polio Eradication Initiative, there were 121 new cases of polio in Nigeria last year, compared to 58 in Pakistan and 37 in Afghanistan.
– Two shootings in northern Nigeria have left nine female polio vaccinators dead, in what is thought to be the latest violence by militant Islamic group Boko Haram, reports the BBC. Both attacks were carried out by gunmen riding on a motor tricycle, though it is not clear yet if the same individuals were involved. Islamic leaders in northern Nigeria have opposed polio vaccinations since 2003, claiming they could lead to infertility and AIDS, reports Reuters. Polio is still endemic in just three countries: Pakistan, Afghanistan, and Nigeria. The shootings happened in and around Kano, the area where 200 children were killed and others maimed by Pfizer's trials of its antibiotic Trovan in 1996.