ISLAMABAD: More than 3.5 million Pakistani children missed out on polio vaccination this week in a campaign overshadowed by the deaths of nine immunisation workers, a UN official said Friday.

The nation of 180 million people is one of only three in the world where the highly infectious, crippling disease remains endemic and infections shot up from a low of 28 in 2005 to almost 200 last year.

Nine people working on the UN-backed program were shot dead in Karachi and in the country's northwest this week, murdered for trying to protect children from a cruel disease that can leave limbs flaccid and useless in a matter of hours.

“Out of a total target of 18.5 million for the last polio round, 14.9 million children were vaccinated throughout the country, resulting in over 3.5 million children missed during the campaign,” Dr Elias Durry, the World Health Organisation's senior coordinator for polio eradication in Pakistan, told AFP.

“WHO and all the partners in polio eradication salute the bravery of thousands of polio team members in the country who performed their duties in the line of fire to reach the 14.9 million children,” he said.

Durry said figures showed 1.75 million children were missed in southern Sindh province after the campaign was called off following the killing of four female polio team members in Karachi, the country's commercial capital.

In the insurgency-hit northwestern Khyber Pakhtunkhwa province, around 700,000 children were missed as a result of the early suspension of the campaign after the deaths of polio team members.

In central Punjab province, more than 800,000 remained unvaccinated but WHO officials said some major cities started the campaign a day late and data were still awaited. It was expected the number of missed children would significantly fall.

More than 200,000 children in different areas remained unvaccinated for reasons unrelated to the attacks.

Efforts to tackle polio in Pakistan have been hampered over the years by local suspicion about vaccination.

The Pakistani Taliban have denied responsibility for the latest attacks though they have threatened polio workers in the past and in June they banned vaccinations in the northwestern tribal area of Waziristan, condemning the drive as a cover for espionage.

Resistance also comes from parents, often poorly educated and impressionable, who believe wild conspiracy theories about the vaccine.