When we think of polio, we usually think of children in braces or requiring a iron lung to breathe. However, the vast majority of poliovirus infections have no symptoms at all. Less than 10 percent have a minor illness with a fever or sore throat. Less than 5 percent have a mild case of meningitis, and around 1 percent have the full-fledged paralysis of certain muscles (polioourelitis). Only about a third of those with paralysis recover completely.