In a huge immunization effort in 150 countries, health teams will on Sunday (April 17) launch what they hope will be the final push against polio.
Stopping transmission of the contagious viral disease that has infected millions is possible within a year, experts say. And full, official, global eradication could be declared by the end of this decade.
First, however, the vaccine that has successfully fought polio for more than 30 years needs to be switched for one that targets the last few areas of risk.
It won’t be easy, or cheap, but the World Health Organization’s director of polio eradication, Michel Zaffran, says failure now - when there have only been 12 cases worldwide this year, in Pakistan and Afghanistan - means the virus could spread across borders again.
Success would make polio only the second human disease to be eradicated since smallpox was banished in 1980.
“Taking our foot off the pedal now could mean polio will within a few years spread straight back into large parts of the world and create 100,000 or 200,000 cases,” Zaffran told Reuters. “The job has not been done and will not be done until we have fully eradicated the virus.”
For the endgame in polio to succeed, a coordinated and complex vaccine switch is crucial.
Until now, many countries have been using a shot that protects against the three types of wild polio virus - type 1, type 2 and type 3 - but type 2 polio transmission has been stopped since 1999, meaning immunizing against it now makes no sense.
In rare cases it also poses a risk that the weakened type 2 virus in the vaccine can seep into circulation and cause “vaccine-derived” polio infections.
So from April 17 to May 1, nearly 150 countries will engage in a synchronized switch to a bivalent, or two-strain, vaccine that contains no type 2 virus but targets types 1 and 3.
It’s a massive undertaking and a major step towards eradication, says Zaffran. “We’re entering into uncharted territory. This has never been done before. But there’s no going back now.”
