Paradoxically, this is because Europe has moved to using a safer vaccine that is crucial to the goal of global polio eradication.

Other epidemiologists argue, however, that Europe and other regions are at no greater risk than before, if a massive vaccination campaign kicking off now stops polio re-establishing itself across the Middle East. If that fails, though, there may be a double peril: polio virus will be more widespread, and there may not be enough vaccine to contain it.

Ten cases of polio have now been confirmed in Syria, where vaccination efforts have collapsed during two years of civil war. Most victims are under two years old. Because polio paralyses only one in 200 unimmunised people infected, that means many more people are carrying and spreading the virus.