Any let up in the fight against polio risks a resurgence of the disease, leading to hundreds of thousands of cases of the deadly virus every year across the globe, one of the world's leading polio experts has warned.
Michel Zaffran, director of global polio eradication at the World Health Organization, told a press conference in advance of World Polio Day on October 24, that the world had never been so close to eradicating the disease, which used to kill and disable hundreds of thousands of children every year.
So far this year there have been just 22 cases of wild poliovirus in Afghanistan and Pakistan, down from a high of more than several hundred thousand cases a year in the 1980s.
“We are extremely close to eradicating wild poliovirus,” said Dr Zaffran. “When we started in 1985 there were over 125 countries where wild poliovirus was endemic and it was causing close to 300,000 cases of paralytic disease every year. We have reached a stage where we are closer than ever before to eradicating the disease.
He added that it was important to chase down the last few cases in order to wipe out the disease for good.
“If we were to stop the effort now and no longer strive to eradicate the wild virus we could see hundreds of thousands of cases every year. We owe it to the children of the world to finish the job,” he said.
Next year, Africa is due to be declared free of wild polio if no new cases are found in Nigeria, the last country in the region to report cases. The last case of the disease was reported in Borno State in the north of the country in 2016.
Ibrahima Koné, technical officer for polio eradication and routine immunisation at Unicef, said that poor security and access had forced Nigeria to be creative in its eradication efforts.
“One example is a strategy called hit and run – as soon as there’s a window of opportunity vaccinators take advantage and rush to the area to vaccinate as many children as possible,” he said.
However, four countries in Africa have reported vaccine-derived polio cases this year: Nigeria, Niger, Somalia and Democratic Republic of the Congo.
When a child is vaccinated the vaccine-virus replicates in the gut, generating an immune response. The vaccine is then excreted and, very rarely, can mutate and spread to other children, especially where vaccination coverage is low. This can then result in outbreaks of polio.
Last week scientists told the Telegraph that polio could not be declared eradicated if cases of the vaccine-derived virus were still circulating.
Dr Zaffran said that it would be "pretty odd" to declare Africa polio free if children are still being paralysed by the vaccine-derived form of the virus.
“But it could still be the case that at the end of next year or early the following year Africa is free of wild poliovirus,” he said. “I hope that the efforts we have already put in place in Democratic Republic of Congo and the Horn of Africa will have succeeded in stopping these outbreaks we currently have because normally they do not last for too long,” he said.
Syria experienced an outbreak of vaccine-derived virus last year, with more than 50 cases of the disease.
“In Syria we had a pretty aggressive set of campaigns which interrupted circulation of the disease in four to five months despite the war. In Somalia we have children who are not accessible in some areas but I believe that we should be able to address these current outbreaks,” he said.
Roland Sutter, coordinator of WHO's polio research, policy and containment team, said that cases of vaccine-derived polio were “a big concern”.
But he added: “The key is achieving very high immunisation coverage in the affected populations just like we would with wild poliovirus.”
Attacks on vaccinators, a lack of security and mistrust have hampered the final eradication efforts in the last two countries reporting cases, with Helmand and Kandahar provinces in Afghanistan proving particularly difficult, said Dr Zaffran.
“Afghanistan is facing tremendous difficulties, however the country and all communities are fully committed to eradicating the disease,” he said. “We need to gain access – consistent access to children in all parts of the country. The surveillance system is extremely good and as soon as we know the virus is circulating, if we are able to access the area we go and vaccinate.”