The global push to immunize children against polio has been an incredible success, reducing polio cases by 99.9 percent.
But there’s a lingering obstacle to a polio-free world: A scant number of people who got one version of the vaccine before it was phased out in 2016 carry a variant of the polio virus that was in that vaccine and has since mutated. The mutated virus can now be passed around in areas where few people have been vaccinated, sickening some along the way.
This is precisely what’s playing out right now, in a very small polio outbreak in the Democratic Republic of the Congo, and with a handful of cases in a few other countries.
This year, DRC has registered no wild polio viruses — that is, polio cases caught from the environment. And Type 2 polio has been completely eradicated in the wild since 1999. But DRC has seen seven cases of Type 2 polio this year that are linked to the vaccine in an outbreak.
The outbreak of vaccine-derived polio was first registered last June, in Maniema province, the central-eastern part of DRC. It has since spread to the south, and popped up in two provinces in the north.
“It’s worrying because it’s spreading,” said Michel Zaffran, director of the polio eradication program at the World Health Organization, who added that the government is not yet taking the outbreak seriously enough. There are, thankfully, stockpiles of the polio-2 vaccine at the ready to confront resurgent outbreaks.