Under police guard, thousands of health workers pressed on with a polio immunisation program after nine were killed elsewhere in Pakistan by suspected militants who oppose the vaccination campaign.
Immunisations were halted in some parts of Pakistan and the UN suspended its field participation everywhere until better security was arranged for its workers. The violence risks reversing recent progress fighting polio in Pakistan, one of three countries in the world where the disease is endemic.
The Taliban have denied responsibility for the shootings. Militants have accused health workers of acting as spies for the US, alleging the vaccine is intended to make Muslim children sterile.
Taliban commanders in Pakistan's troubled northwest tribal region also said earlier this year that vaccinations can't go forward until the US stops drone strikes in the country.
Insurgent opposition to the campaign grew last year after it was revealed that a Pakistani doctor ran a fake vaccination program to help the CIA track down and kill al-Qaida founder Osama bin Laden, who was hiding in the town of Abbottabad in the country's northwest.
There were a few attacks on polio workers in July, but the current level of violence is unprecedented. A polio worker died Thursday after being shot in the head in the northwestern city of Peshawar a day earlier, said health official Janbaz Afridi.
His death raised to nine the number of Pakistanis working on the campaign who have been killed this week. Six of the workers gunned down were women, three of whom were teenagers. Two other workers were critically wounded. All the attacks occurred in northwest Khyber Pakhtunkhwa province and the southern city of Karachi.
Despite the threat, local officials in the eastern city of Lahore continued the vaccination drive Thursday under police escort, said one of the top government officials in the city, Noorul Amin Mengal. About 6,000 Pakistani health workers were escorted by 3,000 police as they fanned out across the city, he said.
"It would have been an easy thing for us to do to stop the campaign," he said. "That would have been devastating."
Saddaf Malik, one of the polio workers in Lahore, said the killings sent a shudder of fear through him and his colleagues.
"We will carry on with our job with determination, but we want the government to adopt measures to ensure the security of polio vaccinators," he said.
This week's killings occurred as the government and the UN began a vaccination drive Monday targeting high-risk areas in the country's four provinces and the semiautonomous tribal region, part of an effort to immunize 34 million children under age 5. The campaign was scheduled to end Wednesday in most parts of the country, except for Lahore, where it ran a day longer.
Government officials ended the drive early in parts of Khyber Pakhtunkhwa and in Sindh province, where Karachi is the capital, said Elias Durry, the UN World Health Organization's senior coordinator for polio in Pakistan. The campaign ran its full course in the provinces of Baluchistan and Punjab, where Lahore is the capital, as well as in the tribal region, he said.
The government has approximately 250,000 people working on the campaign, said Durry. Most of them have other jobs, such as teaching or working as government clerks, and sign on to the vaccination drive to earn a little more money, about $2.50 per day, officials said.
The WHO and UNICEF have about 2,000 people between them who provide technical assistance to the polio teams across the country and educate locals about the program, said Durry and Michael Coleman, a UNICEF spokesman in Pakistan. The UN staff were pulled out of the field and asked to work from home Wednesday.
Workers were only able to immunize about 9 million children this week out of a target of 18.3 million because of the violence, said Durry.
Polio usually infects children living in unsanitary conditions, attacks the nerves and can kill or paralyse. Pakistan, Afghanistan and Nigeria remain the last battlegrounds for the fight against the disease.
There is no history of attacks on polio workers in Afghanistan, even though the country also faces a domestic Taliban insurgency. Muslim leaders in Nigeria have spoken out against polio vaccination in the country in the past, also claiming it makes children sterile. Many now support the campaign, but some Nigerians remain suspicious.
Prevention efforts have managed to reduce the number of cases in Pakistan to 56 this year, compared with 190 in 2011, a drop of about 70 per cent. Most of the news cases in Pakistan are in the northwest, where the presence of militants makes it difficult to reach children. Clerics and tribal elders have been recruited to support polio vaccinations to try to open up areas previously inaccessible to health workers.
Israrullah Khan, a villager who attended the funeral of the polio worker who died Thursday, said most of the clerics and Islamic political parties in Khyber Pakhtunkhwa were in favour of the campaign.
"We don't understand why these attacks have suddenly started," Khan said. "It's very sad because they were trying to save our children's future for very low wages."