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Story highlights

NEW: Official: Parents who sign affidavit vowing to vaccinate their children will be released

Pakistan has more new polio cases than any other country

Militants have targeted health workers administering vaccines for years

(CNN) —  

Police have arrested more than 500 parents in and around the northwestern Pakistani city of Peshawar for not allowing their children to get the polio vaccine, an official said Tuesday.

Peshawar Deputy Commissioner Riaz Khan Mehsud told CNN that the 513 arrests took place Monday and Tuesday as part of a government campaign to administer polio vaccines in parts of Pakistan’s Khyber Pakhtunkhwa province.

Those arrested will be released on bail if they sign an affidavit stating that they will let their children get vaccinated, according to the deputy commissioner.

Pakistan’s vaccination rate is inordinately low for a number of reasons, including attacks on medical workers, the displacement of people due to ongoing military operations and a lack of trust by some families.

Whatever the reason, the fact that a large number of children are not immunized is having an impact.

Such vaccines are credited with wiping out polio in most parts of the world. But Pakistan is an exception, according to the Global Polio Eradication Initiative, a public-private partnership that includes the World Health Organization and United Nations Children’s Fund (UNICEF). The South Asian nation leads all others in new polio cases in recent years, and has nine of this year’s 10 reported cases.

In 2014, Pakistan had 327 cases. The next closest country was Nigeria, with 36 cases.

Authorities in Khyber Pakhtunkhwa province hope to ensure that 2.7 million children there get vaccine drops. They’ve learned about more than 13,000 cases in which parents have not done so since a provincial campaign began two weeks ago, Mehsud said.

Dr. Bilal Ahmad, a UNICEF team leader based in Pakistan, called authorities’ unprecedented move a last-ditch effort to clear polio from “cluster” zones where large numbers of families have refused to get their children vaccinated.

“First the workers (try to) convince them, then their supervisors, then senior members of the community,” Ahmad said. “(This government action) is the final step in eradicating this issue.”

Polio is a highly infectious viral disease that primarily affects young children, sometimes leading to paralysis and death. The virus is easily preventable through immunization, but there’s no cure once it is contracted.

It went from being a health issue to a security issue after U.S. intelligence officials used a vaccination program to help in their hunt for Osama bin Laden in 2011. Under cover of the program, the CIA sought to collect DNA samples from relatives of the al Qaeda leader to verify his presence in a compound in Abbottabad, Pakistan.

CIA policy: Won’t use vaccination programs as part of operations

Those administering the vaccines have become targets, with the National Emergency Operations Center reporting that more than 70 medical workers have been killed in attacks since December 2012.

And in June 2012, Pakistani Taliban commander Hafiz Gul Bahadur announced that polio vaccines would be banned in another Pakistani province – North Waziristan – because of drone strikes there. Bahadur called the strikes “worse than polio.”

CNN’s Sophia Saifi reported from Islamabad, and CNN’s Greg Botelho wrote this report from Atlanta.