Polio has spread to three countries this year . No other country has reported more than four cases , and the only country with four was Afghanistan , he said . It 's typically the low season for transmission of the virus . Comment: 417 cases of polio were reported worldwide in 2013 , WHO says .
Polio has spread to three countries this year . It 's typically the low season for transmission of the virus . Comment: 417 cases of polio were reported worldwide in 2013 , WHO says .