The country is one of only two in the world where polio is still a serious problem.

Vaccination teams in the southern port city of Karachi went door to door, flanked by armed police, administering polio drops into children's mouths without touching them, in line with new coronavirus safety guidelines.

"Right now we can't say what impact the four-month suspension will have on our fight against polio, but one thing is sure -- that the current year is going to be worse than the previous years in regard to the number of new cases," Zulfiqar Babakhel, a spokesman for the country's vaccination authority, told AFP. 

As well as the pause to the campaign, a further 2.8 million newborns also missed out on polio vaccinations, he said.

Muhammad Nadeem, a 63-year-old shopkeeper from Karachi, said his family had been waiting anxiously for their two-year-old son to be vaccinated against the highly infectious disease.

"It is a matter of our son's future, and today we are finally feeling relieved after four months of fear and impatience," he said.

The drive will first target 800,000 children under the age of five in districts where polio is in continuous circulation -- including in parts of Quetta, Karachi and Lahore -- before broadening to a nationwide campaign by the end of the year.

Health minister Zafar Mirza said the program was restarting as a result of the coronavirus situation in Pakistan improving. 

Authorities have declared more than a quarter of a million coronavirus cases, although with low testing the true figure is expected to be much higher.

Rana Muhammad Safdar, who is leading the polio eradication program, said the temporary suspension had "widened the immunity gap among vulnerable children significantly".

Gains made at the start of year had been reversed, he added, after cases jumped to 147 in 2019, up from 12 in 2018.

So far this year 60 cases have been reported, but experts said the impact of the pause could take months to emerge.

The United Nations children's agency UNICEF warned in May that millions of children were at risk of diseases such as diphtheria, measles and polio after the coronavirus pandemic disrupted routine immunization services around the world.

Pakistan is one of only two countries where polio remains endemic. The other is neighboring Afghanistan, where last month officials detected the disease in areas previously declared free of it, following a similar pause in vaccinations.

Inoculation teams in both countries are often viewed with suspicion.

Opposition grew after the CIA organized a fake vaccination drive to help track down Al-Qaeda's former leader Osama bin Laden in the Pakistani city of Abbottabad.

As Pakistan has tried to eliminate polio, a new challenge has emerged in the form of a growing global movement against vaccinations.

The phenomenon has attracted adherents worldwide, fuelled by medically baseless claims and proliferated on social media, resulting in a resurgence of once-eradicated, highly contagious diseases.