Polio might just be looking at a comeback tour, thanks to the Syrian civil war

There's a significant risk that the now-rare disease could spread from Syria to Europe, as refugees seek asylum there, a group of German scientists have warned. The danger is that many people may not know they're carrying the disease; only about 1 in 200 people infected develop symptoms. The vaccine commonly known in Europe exacerbates this, because it's good at preventing symptoms but only partially effective at preventing infection. It could take almost a year of silent transmission before the outbreak is detected, although hundreds of individuals would carry the infection. Simply vaccinating Syrian refugees is insufficient. This is one reason why you want to keep refugees out of your country.