At the foot of Margalla’s lush green hills, outside Islamabad, lies an almost impenetrable building surrounded by barriers, armed guards and sniffer dogs. Visitors are extensively searched before being allowed inside.

It could be an army barracks. It is, in fact, Pakistan’s National Emergency Operation Centre, and the headquarters of its polio eradication programme.

Babar Atta, Pakistan’s most senior government official in charge of the programme, talks to me in his office surrounded by charts and graphs. On the wall is a giant map marked with coloured pins to indicate the country’s high risk areas.

Despite the recent setbacks, Pakistan’s polio programme has achieved significant success over the last 25 years.

But any programme of this size would be vulnerable to difficulties.

In Pakistan, there are more than 40 million children under the age of five, according to Atta. The government says an average of 500,000 children remain missing from national campaigns, but Atta believes the number is far higher.

“If the polio virus is still present in our environment, it points to just one thing - that we are missing a large number of children in every campaign.”

Children who have been vaccinated are given ink marks on their fingers. But polio vaccine ambassador Abrar had suggested to me that polio workers were marking the fingers of children who hadn’t been vaccinated, to inflate numbers.

Atta agrees this could be happening.

“I have worked in Pakistan’s polio programme for eight years, and I was the one who identified fake finger marking,” he says.

He says one of the reasons the Pakistani public is so suspicious of the polio vaccination programme is because the CIA fake vaccine scandal created such a backlash.

The CIA and doctor accused of being involved have always denied the scheme took place but the Pakistan authorities are adamant it did, and Afridi remains in jail.

“It created mistrust among people - they ask why the West, particularly the US, is so bothered about polio in Pakistan? We will have to de-link the polio programme from the West if we want to make it successful.”

And he is determined to signal that the government will not tolerate fake news surrounding the vaccine. A few weeks after I visited him he announced the government had suspended seven schools in Peshawar found to have been involved in creating “mass hysteria” over the vaccine in April.

Atta is adamant that the key to success is to win parents’ hearts and minds.

“We need to win people over. It’s the parents’ right to ask questions, and it’s the government’s responsibility to respond to them.”

Back on the streets this is down to polio workers like Gulnaz to wrestle with parents’ fears. And in Pakistan’s battle with polio, fear is all too often followed by violence.

“I don’t feel intimidated any more, because I am not alone in this. There are people who are working in more dangerous areas and are doing a far better job. I get a lot of strength from my colleagues, and Allah is with me. I like this job; my heart finds solace in it,” she says.