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. 
 
 In the first attack in Kano the polio vaccinators were shot dead by gunmen who drove up on a motor tricycle. 
 
 Thirty minutes later gunmen targeted a clinic outside Kano city as the vaccinators prepared to start work. 
 
 Some Nigerian Muslim leaders have previously opposed polio vaccinations, claiming they could cause infertility. 
 
 On Thursday, a controversial Islamic cleric spoke out against the polio vaccination campaign, telling people that new cases of polio were caused by contaminated medicine. 
 
 Such opposition is a major reason why Nigeria is one of just three countries where polio is still endemic. 
 
 But this is believed to be the first time polio vaccinators have been attacked in the country. 
 
 Some Kano residents told the BBC's Yusuf Yakasai in the city that other people injured in the first attack had been taken to hospital. 
 
 A health official confirmed to the BBC that those killed in the second attack in Hotoro were female health workers - there were earlier reports that people waiting at the clinic may have been among those shot. 
 
 Witnesses in Hotoro told the BBC gunmen also approached the health centre using a motor tricycle. 
 
 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. 
 
 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. 
 
 Analysts believe the attacks may have been the work of the militant Islamist group Boko Haram but it has not yet commented and no group has said it carried out the attack. 
 
 The group - whose name translates as "Western education is forbidden" - says it is fighting to overthrow the government and impose Sharia. 
 
 It has been blamed for the deaths of some 1,400 people in central and northern Nigeria since 2010. 
 
 According to the Global Polio Eradication Initiative, there were 121 cases of polio in Nigeria last year, compared to 58 in Pakistan and 37 in Afghanistan. 
 
 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. ||||| KANO, Nigeria 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 on Friday, police said. 
 
 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. 
 
 Some influential Muslim leaders in Kano openly oppose polio vaccination, saying it is a conspiracy against Muslim children. 
 
 The attacks will hit efforts by global health organizations to clear Nigeria's mostly-Muslim north of polio; a virus that can cause irreversible paralysis within hours of infection. 
 
 It is the second time this year that polio workers have come under attack by Islamist militants after gunmen killed aid workers tackling the disease in Pakistan last month. 
 
 "Gunmen on bikes opened fire on a health center in the Hotoro district killing seven, while an attack on Zaria Road area of the city claimed two lives," said police spokesman Magaji Musa. 
 
 "They were working for the state government giving out polio vaccinations at the time of the attack," Musa added. 
 
 Kano government banned motorbikes from carrying passengers last month after the Emir of Kano, one of the country's most prominent leaders, was nearly killed when gunmen attacked his convoy, killing four of his aides. 
 
 Kano residents said soldiers had cordoned off the areas attacked and movement was being restricted in the city. 
 
 ISLAMIST THREAT 
 
 Boko Haram killed hundreds last year as part of its campaign to impose Islamic law, or sharia, on a country of 160 million split roughly equally between Christians and Muslims. 
 
 The group is seen as the most serious threat to the stability of Africa's top energy producer, and Western governments fear the country could become a base for operations of al Qaeda-linked Islamist groups in the Sahara. 
 
 President Goodluck Jonathan has highlighted links between Boko Haram and Saharan Islamists and said that relationship justified his decision to join efforts by French and West African forces to fight militants in Mali last month. 
 
 In 2003, northern Nigeria's Muslim leaders opposed polio vaccinations, saying they could cause infertility and AIDS. 
 
 Their campaign against the treatments was blamed for a resurgence of the disease in parts of Nigeria and other African countries previously declared polio-free. 
 
 Polio, a virus that attacks the nervous system, crippled thousands of people every year in rich nations until the 1950s. 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. 
 
 "This is certainly a setback for polio eradication in Nigeria, but not a stop," said Oyewale Tomori, a campaigner for polio eradication in Nigeria. 
 
 "The best we can do is to work harder and see the end of polio ... so their loss will not end as a useless sacrifice." 
 
 At least 16 health workers taking part in polio vaccination drives were killed in attacks in Pakistan in December and January. 
 
 Local Taliban militants said they did not carry out those attacks although its leaders have repeatedly denounced the vaccination program as a plot to sterilize people or spy on Muslims. 
 
 (Additional reporting by Joe Brock and Mike Oboh in Abuja; Writing by Joe Brock; Editing by Jon Hemming)
– 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.