As health workers last week picked their way through the grimy lanes of one of Karachi's poorest slums, the virtual world of social media platforms would at first glance appear to pose little threat to their work.
Five years ago the women going door-to-door to distribute vaccines in a bid to eradicate polio defied the real physical threat of motorbike-riding militants who gunned down health workers across Pakistan.
That violence has thankfully receded, but the campaign to wipe out the crippling viral disease from one of its last haunts has this year instead faced a very 21st century challenge.
Each of the community workers knows when they knock on a door to vaccinate children inside, there is a chance parents will refuse because of a bogus video shared online which claims that the drops are deadly.
Last week a network of 250,000 workers accompanied by tens of thousands of police swung into action across Pakistan, as it does every month in a regular five-day vaccination drive.
Their efforts mean we now have 16 million children globally who are not paralysed and are running about enjoying normal lives.
Dr Chris Elias, Global Polio Eradication Initiative
Misconceptions inflamed on social media are one of the last hurdles for Pakistan to eliminate a disease which has nearly been pushed to extinction.
Such is the power of the social platforms that a video wrongly claiming polio drops killed 16 children in March led to a spike of tens of thousands of parents refusing vaccines in Karachi alone.
“Cell phones are so cheap now and they all use Facebook, WhatsApp and so on. People can sit at home, make their own video, and put it out and it goes viral,” explained Zakir Khan, a 29-year-old communications official working on the campaign in the Mustafabad neighbourhood.
“People would show us videos as soon as we enter the house and say because of your vaccines, 16 people have died. Why are you coming to my house?”
May's campaign saw the number of refusals to take drops more than double in Karachi to 70,000, with the fake video blamed for most of that increase.
The damage was largely done by a simple phone clip shot in the city of Nawabshah. The town had just seen three children die after a string of alleged medical blunders by a health worker trying to give them a measles vaccine. But the unknown man filming mourning crowds instead blames polio and says 16 children died. Within days of being shot, the clip had spread faster than any disease outbreak.
“We tried to tell people whatever social media says is not necessarily true,” said Seema Adel, a 21-year-old supervisor who with 42 colleagues has the target of vaccinating 8,900 children in Hijrat colony.
“We had some serious refusals in my areas because of that video. Around 45 kids were refused just because of that film.”
Days and sometimes weeks of patient persuasion eventually changed the minds of most who had refused and the early signs from last week's campaign were that the harmful video had lost some of its power.
But misconceptions remain one of the campaign's largest problems, said Fayaz Ahmed Jatoi, who coordinates the programme for Sindh province.
“Social media is kind of one big phantom which we have never been able to be on top of,” he explained.
Pakistan's authorities are not the only ones in the region battling dealing with the issue.
Last week Indian authorities asked WhatsApp to take “immediate action” to halt a spate of village mob lynchings inflamed by false viral rumours on the platform.
WhatsApp has now offered $50,000 (£37,800) to anyone who can help stop the spread of fake news on its platform following the lynchings.
Pakistan's struggle with social media comes as the decades long battle to eradicate polio globally moves towards its climax. If successful, it will be only the second disease in history to have been wiped out - the first was smallpox, which was declared eradicated in 1980, three years after the last recorded case.
The polio virus now only remains in Pakistan, Nigeria and Afghanistan. Those three countries have seen only 11 cases so far in 2018, compared to 22 last year. That marks a fall of well over 99 per cent from the 350,000 annual cases when the global eradication drive began in 1988.
Afghanistan and Pakistan are likely to be the “wild” virus's last stand.
The only African region where it clings on is the northeast of Nigeria, where a bloody Islamist insurgency by the Boko Haram militant group has rendered the region inaccessible to aid and health workers. Even so, there have been no cases since 2016.
A small number of cases have come from so-called vaccine-derived outbreaks where weakened virus used in drops to build immunity has gradually mutated back to its dangerous form.
This has happened in the Democratic Republic of Congo, where decades of war and instability have resulted in a large population of unvaccinated children — a perfect breeding ground for the vaccine-derived virus to spread. Nearly 30 cases of polio have been diagnosed across several regions in the east of the country in the latest outbreak.
Threats have emerged elsewhere. Polio was discovered in sewage samples taken from a suburb of the Kenyan capital Nairobi last month, prompting a large vaccination drive. Swifter interventions in more stable African states have stopped the virus from spreading. Kenya, for instance, has reported no actual polio cases since 2014.
Pakistan itself has made strides in recent years after seeing 306 polio cases as recently as 2014. Health workers back then faced a bloody Taliban campaign claiming vaccination was a Western plot to sterilise Muslim children.
Public suspicion was heightened by the disclosure that the CIA had organised a fake vaccination campaign to gather DNA samples in the hunt for Osama bin Laden.
Between 2012 and 2014 around 100 vaccinators and police are thought to have been killed on polio duty. In the campaign's Karachi headquarters are posters of 10 young men and women killed in the city at the time.
But the country's campaign was also badly organised and furious international monitors in 2014 bluntly declared it a “disaster”. A worldwide summary of eradication efforts at the time said the country continued “to flounder hopelessly, as its virus flourishes”.
Stung by the criticism, the country overhauled its efforts, set up a series of emergency operations centres and decided to rely only on local women to form the frontline workforce of vaccinators.
With the new workforce accepted and trusted by their communities, much of the suspicion evaporated. Each worker now also carries a book of decrees from senior clerics endorsing the campaign, which has greatly reduced religious objections.
Successful army operations to clear Taliban militants from the border tribal regions have also given health workers access to areas previously impossible to reach. Attacks on workers have declined as the militants' power has waned, though they have not gone away completely.
A mother and daughter who were administering polio vaccinations in the south-western city of Quetta were shot dead in January.
The intensity of the galvanised campaign has caused its own discontent. To ensure the virus is wiped out not only from children but also from the environment where it can hide and circulate, workers set out monthly to give drops to every child under five in their area.
As months pass and children are vaccinated again and again, perhaps dozens of times, workers find growing fatigue on the doorstep. Only patient persuasion wins in the end, said Naureen Amjad, a 39-year-old health worker in Hijrat colony. “Even if I have to go 10 times, then I will go.”
The scale of the operation is vast. In Karachi alone 23,000 health workers are trying to find and vaccinate 2.4 million children in five days. But despite the obstacles, the vaccination rate now hovers close to the 95 per cent level thought to be necessary to wipe out the disease.
As well as misconceptions, the porous border with Afghanistan remains the most difficult barrier to overcome. The constant traffic across the border means the two nations are effectively one pool of cases and the difficulty of vaccinating in Afghanistan's conflict zones is a headache for Pakistan.
In London last week, Dr Chris Elias, chair of the Polio Oversight Board of the Global Polio Eradication Initiative, described the drive to eradicate polio as a “long slog” but said the bravery of vaccine workers on the ground kept him optimistic the war against the virus would soon be won.
“Their efforts mean we now have 16 million children globally who are not paralysed and are running about enjoying normal lives. The value in that is incalculable”, he said.
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