Israel is in the midst of a massive, emergency immunization drive of all children under the age of 9 against polio.
Why?
Health
 workers detected the virus in southern Israel in February. Since then, 
they've found it in 85 different sewage samples across the country, the 
 said Wednesday. Yet so far, no children have gotten sick or been 
paralyzed by the virus.
Israel has one of the highest rates of 
 immunization coverage in the world, says Chris Maher of the World 
Health Organization. And that's one reason why the country has avoided 
polio cases, so far. But health officials are still very concerned about
 the situation.
The vaccination campaign aims to give polio boosters to a million children.
"There's
 no way that 100 percent of the population can be immune at any given 
time," Maher says. "So any time that virus is circulating [in the 
environment], if there's a person who's not immune, there's a risk that 
that person is going to get clinical polio. They're going to get 
infected, and they're going to get sick."
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