Sixty years ago, parents in Europe and America lived with the dread that their children might be paralysed by polio. After Dr Jonas Salk produced a vaccine against infant paralysis in 1955, that fear subsided -  all children were immunised and the disease was eradicated in the west.

Today, most of the world is  polio-free but the disease remains endemic in just three countries: Pakistan, Afghanistan and Nigeria. Other countries are equally poor, with comparably weak health systems, but what distinguishes these three is that extremist Islamist preachers have tried to disrupt polio eradication.

If you look at the map, you can see that the cases in Nigeria are nearly all in the north where preachers allied to the terrorist group Boko Haram operate. In the last two days, five health workers on a three-day polio drive in Pakistan have been shot and killed – four in Karachi and one in Peshawar. The latter was a 17-year-old girl.

It seems extraordinary that anyone could campaign against saving children from death and disability, but in June militants in Pakistan’s tribal areas issued a fatwa saying they wouldn’t allow health workers to vaccinate children unless US drone strikes stopped.

In other words, they saw saving Pakistani children as something the Americans want to do, a bargaining chip in their conflict with the infidel. Other extremists claim that vaccination is a secret American plot to sterilise Muslims.

But the Americans also bear some responsibility. Last year, the CIA employed a Pakistani doctor, Shakeel Afridi, to conduct a fake hepatitis B campaign in Abbottabad where Osama bin Laden was hiding.

His real job was to get bin Laden’s DNA so the Americans could be sure that they were targeting the  right man. Dr Afridi has been imprisoned for treason, and aid agencies are furious that their genuine vaccination campaigns may have been compromised.

“For us as a humanitarian organisation and for health care workers all around the world, that kind of abuse puts the cross-hairs on our back,” said Mark DuBois, Executive Director of Medecins sans Frontieres UK. “If people stop trusting us, if they think we’re there to help the military purpose of western governments then we’re not able to access those people.”

It’s hard enough for health workers to operate in countries like Pakistan and Afghanistan, where westerners and those who work for western aid agencies already struggle to explain that they’re separate from their governments. By using a vaccination campaign as a cover, the CIA made polio eradication that much harder.

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