PESHAWAR, Pakistan Three workers in a polio eradication campaign were shot in Pakistan on Wednesday, and two of them were killed, the latest in an unprecedented string of attacks over the past three days that has partially halted the U.N.-backed campaign. 
 
 The United Nations in Pakistan has pulled all staff involved in the campaign off the streets, spokesman Michael Coleman said. 
 
 The government said immunization was continuing in some areas without U.N. support although many workers refused to go out. Women health workers held protests in the southern city of Karachi and in the capital, Islamabad. 
 
 "We go out and risk our lives to save other people's children from being permanently handicapped, for what? So that our own children become orphans?" health worker Ambreen Bibi said at the Islamabad protest. 
 
 The government was caught off guard by the violence, saying they had not expected attacks in areas far from Taliban strongholds and they would have to change tactics in the health campaign. 
 
 "We didn't expect such attacks in Karachi," said Mustafa Nawaz Khokhar, minister for human rights, who oversees the polio campaign. He was referring to the southern commercial hub where there have been attacks this week. 
 
 "In far flung areas where the threats are more pronounced, we have been providing polio teams security." 
 
 Wednesday saw four separate attacks, all in the north. In the district of Charsadda, men on motorbikes shot dead a woman and her driver, police and health officials said. 
 
 Hours earlier, gunmen wounded a male health worker in the nearby provincial capital of Peshawar. He was in critical condition, said a doctor at the Lady Reading Hospital where he is being treated. 
 
 Four other women health workers were shot at but not hit in nearby Nowshera, said Jan Baz Afridi, deputy head of the Expanded Programme on Immunisation. Two women health workers were shot at in Dwasaro village in Charsadda, police said. 
 
 It was not clear who was behind the violence. 
 
 Many Islamists, including Taliban militants, have long opposed the campaign. Some say it aims to sterilize Muslims, while one militant commander said it could not continue unless attacks by U.S. drone aircraft stopped. 
 
 The Taliban have repeatedly threatened health workers involved in the campaign. Some said they received calls telling them to stop working with "infidels" just before the attacks. 
 
 But a spokesman for the Pakistani Taliban, Ihsanullah Ihsan, told Reuters his group was not involved in the violence. 
 
 "BETTER COORDINATION" 
 
 On Monday and Tuesday, six health workers were killed in attacks in the southern port city of Karachi and in Peshawar. Five were women and the youngest was 17. 
 
 Five of the shootings happened in Karachi, home to 18 million people. Health authorities there suspended the polio eradication campaign in the entire province of Sindh. 
 
 Karachi police spokesman Imran Shaukat said teams were supposed to tell police of their movements but had not done so. 
 
 "There has to be better coordination between the health department and police," he said. "We have decided that we will be more forthcoming and contact polio team heads ourselves." 
 
 Minister Khokhar said the drive would resume as soon as security was in place. 
 
 "The teams go into every little neighborhood. You can understand that enormous resources are needed if we have to protect each and every team and worker, which we will have to now," he said. 
 
 On Wednesday, police said they killed two people and arrested 15 during raids connected to the shootings. 
 
 Authorities in the northern Khyber Paktunkhwa province, the capital of which is Peshawar, said they would not accept the U.N.'s recommendation to suspend the campaign. 
 
 "If we stopped the campaign it would encourage the forces opposing the polio vaccination," said provincial official Javed Marwat. 
 
 But their insistence the campaign continue angered health workers who said their colleagues told officials in Charsadda about threats before Wednesday's shootings. The officials insisted the vaccinations take place anyway. 
 
 Khokar said Taliban hostility to the campaign increased after it emerged that the CIA had used a fake vaccination campaign to try to gather information about Osama bin Laden, before he was found and killed in a Pakistani town last year. 
 
 Pakistan had 20,000 polio cases in 1994 but vigorous vaccination efforts had brought the number down to 56 in 2012, the government said. 
 
 A global vaccination campaign has eradicated the disease from everywhere except Pakistan, Afghanistan and Nigeria. 
 
 Polio can paralyze or kill within hours of infection. It is transmitted person-to-person, meaning that as long as one child is infected, the disease can be passed to others. 
 
 (Additional reporting by Mehreen Zahra-Malik in Islamabad and Imtiaz Shah in Karachi; Writing by Katharine Houreld; Editing by Michael Perry and Robert Birsel) 

 Media playback is unsupported on your device Media caption Bruce Aylward, World Health Organisation: Attacks "absolutely horrific" 
 
 Two polio vaccination workers have been killed in north-western Pakistan in the latest of a spate of deadly attacks. 
 
 The shootings in the Peshawar region left a vaccination supervisor and her driver dead, and injured a volunteer. 
 
 The deaths brought to eight the number of health workers killed in this week's anti-polio drive. The three-day drive is now over. 
 
 No group has claimed responsibility, but the Taliban have issued threats against the UN's anti-polio efforts. 
 
 The militants have accused health workers of working as US spies and say the vaccine makes children sterile. 
 
 Pakistan is one of just three countries where the disease is still endemic. 
 
 Coming after five deaths on Tuesday, and one on Monday, the UN children's agency Unicef and the World Health Organisation halted work in Sindh province in the south and Khyber Pakhtunkhwa in the north-west on Tuesday. The suspension was extended nationwide on Wednesday. 
 
 The UN provides technical and financial support to employees and volunteers of the local health departments who administer the polio drops. 
 
 Despite the killings, the immunisation drive continued in some areas on Wednesday - although a number of local health workers refused to go out, Reuters news agency reported. 
 
 'We risk our lives' 
 
 In Wednesday's violence, the vaccination supervisor and her driver died when their car was sprayed with bullets by gunmen riding motorbikes in Charsadda district, north-east of Peshawar, police said. 
 
 The student volunteer was shot in the head and critically injured when gunmen on two motorbikes fired at a team of vaccinators in a northern suburb of Peshawar. 
 
 Polio's last stand? 2012 cases Nigeria - 97 
 
 Pakistan - 47 
 
 Afghanistan - 26 
 
 Chad - 5 Source: IMB Polio killings a major setback 
 
 Gunmen riding motorbikes also shot at polio vaccinators in another area of Charsadda and in the adjoining district of Nowshera, although no injuries were reported. 
 
 On Tuesday, four female health workers were shot dead in the space of 20 minutes in Karachi, and a fifth woman died after being shot in Peshawar. A day earlier a male health worker working on the anti-polio drive was also killed in Karachi, although police have suggested other factors may also lie behind his death. 
 
 Correspondents say the authorities were caught off guard by the violence - until now most attacks on health workers have taken place in north-western areas near militant strongholds. 
 
 At a rally in Islamabad, health worker Ambreen Bibi told Reuters: "We go out and risk our lives to save other people's children from being permanently handicapped, for what? So that our own children become orphans?" 
 
 Wednesday was the final day of a three-day nationwide anti-polio drive - during which an estimated 5.2 million polio drops were to be administered. 
 
 There has been opposition to such immunisation efforts in parts of Pakistan, particularly after a fake CIA hepatitis vaccination campaign helped to locate Osama Bin Laden in 2011. 
 
 Militants have kidnapped and killed foreign NGO workers in the past in an attempt to halt the immunisation drives, which they say are part of efforts to spy on them. 
 
 Polio facts Highly infectious viral disease 
 
 Transmitted via contaminated faeces 
 
 Can cause irreversible paralysis, usually in the legs 
 
 A minority of cases are fatal 
 
 Afghanistan and Nigeria are the only other countries where polio is still endemic. 
 
 Pakistan is considered the key battleground in the global fight against the disease, which attacks the nervous system and can cause permanent paralysis within hours of infection. 
 
 Almost 200 children were paralysed in the country in 2011 - the worst figures in 15 years. 
 
 Earlier this year, the Global Polio Eradication Initiative warned that tackling the disease had entered "emergency mode" after "explosive" outbreaks in countries previously free of polio. 
 
 The World Health Organization said polio was at a tipping point, with experts fearing it could "come back with a vengeance" after large outbreaks in Africa and Tajikistan, and China's first recorded cases for more than a decade. 
 
 Declaring polio a national emergency, the Pakistani government is targeting 33 million children for vaccination with some 88,000 health workers delivering vaccination drops.
– The UN and WHO are suspending an anti-polio campaign in Pakistan as the attacks against polio vaccination workers continue, with a total of eight dead in just two days and more injured. The latest attacks in the Peshawar region today killed a supervisor and her driver and critically injured a student who was volunteering with the campaign, the BBC reports. Other health workers were shot at, but not hit. Six workers were killed in attacks Monday and yesterday. The UN has pulled all vaccination staff off the streets, Reuters reports. Pakistani officials say the immunization campaign is ongoing in some areas despite a lack of UN support, but many workers are refusing to participate and some are holding protests. Though no group has claimed responsibility for the attacks, the Taliban is assumed to be behind it. Immunization drives are controversial in Pakistan after the CIA ran a fake hepatitis vaccine campaign in order to track down Osama bin Laden.