PESHAWAR: While vaccine distrust has sparked debates amid a measles outbreak in the United States, Pakistan is in a deadly battle to wipe out polio.

Long eradicated in the West, polio remains endemic in Pakistan after the Taliban banned vaccinations, attacks targeted medical staffers and suspicions lingered about the inoculations.

The persistence of this crippling, sometimes fatal virus shows just how difficult wiping out a disease can be, even amid campaigns seeing thousands of vaccinators go into the field to offer polio drops to children, sometimes under armed guard.

Read: Lost — The battle against polio

“When we leave in the morning, we do it at the risk of our life,” vaccinator Rubina Iqbal said. “We don't know whether we will come back alive or not. “

Polio is a highly contagious virus generally transmitted in unsanitary conditions.

There is no cure for the virus, which mostly affects children under 5, though it can be prevented with a vaccine.

In the US, polio terrified mothers and fathers as outbreaks caused more than 15,000 cases of paralysis each year until Dr Jonas Salk invented a vaccine in the 1950s.

After eradicating smallpox in 1980, authorities turned their attention to polio.

In Pakistan, the disease, and the backlash against vaccinations, is mostly in its northwest and the port city of Karachi, although the vaccination drive is country-wide.

The scope of the vaccinators' efforts in Pakistan is impressive.

In January, officials targeted some 35 million children during a nationwide campaign, said Dr Rana Muhammad Safdar, who oversees the country's polio emergency operations center.

Smaller campaigns are held more frequently in areas where the virus is believed to be especially prevalent. Workers at central bus stops and train stations also vaccinate child travelers.

Neighboring India was declared polio-free in 2014, a massive logistical feat for the country of 1.2 billion people.

Many experts thought success was near in Pakistan in 2012 but then the number of cases shot up last year.

But instead of parents' groups worried about autism and celebrities relying on a discredited scientific article like in the US, Pakistan's anti-vaccine campaign has been waged at the end of the barrel of an assault rifle.

Also read: American NGOs assail CIA over fake vaccination drive

The Pakistani Taliban banned vaccinations in 2012 after US Navy SEALs launched a raid in Abbottabad in 2011 that killed al Qaeda leader Osama bin Laden.

Ahead of the raid, the CIA sent in a local doctor who claimed to be conducting a hepatitis vaccine program to collect DNA from children at bin Laden's home.

That sparked widespread distrust, in a country where many also fear the inoculations are a plot to sterilise Muslim children.

Also read: The desperate struggle of Pakistan's polio 'martyrs'

By December 2012, militant gunmen began targeting vaccination teams in what became a “horrendous serial killing,” said Elias Durry, the World Health Organization's point person in Pakistan on polio.

An estimated 75 people involved in Pakistan's vaccination efforts have been killed since, Safdar said.

On Tuesday, authorities in Pakistan's Baluchistan province found the bullet-riddled bodies of four people who disappeared Saturday while preparing for a polio campaign.

Also read: Two polio workers, two Levies men found dead

Infected children and others who travel outside of the region can lead to fresh outbreaks in cities, and even other countries, where polio has already been wiped out.

Outside of Pakistan, only Afghanistan and Nigeria are countries where polio remains endemic.

To fight polio, Pakistan's government has created emergency operations centers in Islamabad and provincial capitals where officials meet daily, a tactic that helped immensely in Nigeria.

In certain high-risk areas they introduced a longer-lasting, injectable vaccine instead of oral drops.

Also read: All-out military operation launched in North Waziristan

A Pakistani military operation launched in June in the North Waziristan tribal area also allowed vaccinators to finally access children there after hundreds of thousands of people fled the region and settled elsewhere in Pakistan.

Vaccinators in November also started going door-to-door in South Waziristan for the first time in two years, and the intensity of attacks against vaccination teams has slowed, Safdar said.

The number of people outright refusing the vaccine has dropped, officials say.

Officials also have implemented new security strategies to protect vaccinators.

“By this time last year, nobody could go to North Waziristan. ... Vaccinators were being killed left and right,” Durry said. “So those issues are improving, and have improved dramatically.“

Vaccinators say they use their own arguments to convince reluctant residents, such as talking about how they give the drops to their own children.

However, they can also quickly recall stories of being harassed on the job.

In northwest Pakistan many people are suspicious of women working outside the home.

Bureaucratic challenges also beset the vaccination drive.

Vaccinators complain they don't get paid on time.

Polio workers in the Bajaur tribal area recently protested, saying they hadn't been paid for five months.

To change that, paychecks are now deposited directly into vaccinators' bank accounts, Safdar said.

But delays still happen, he said.

Pakistani officials also are reaching out to the religious community for help convincing people to take the vaccine.

Imams like Mohammad Israr Madni, who teaches at the influential Haqqania religious school in the northwestern city of Nowshera, are part of those efforts. “I want to reach every madrassa, every mosque, to convince (Muslim scholars) and pave the way for awareness among people,” Madni said.