Polio is a serious condition that causes paralysis. However, this occurs in less than 1% of those infected (paralytic polio). Most people do not become sick at all. In a small number of cases, the disease causes flu-like symptoms but does not lead paralysis (non-paralytic polio).
Non-paralytic polio causes symptoms that mimic the flu. A person may experience a sore throat, fatigue, nausea, diarrhea, a fever, or vomiting. Most cases of non-paralytic polio clear up in a number of days, but some people go on to develop meningitis, a condition in which the lining of the brain is infected. Meningitis can be fatal if it is not treated quickly.
When a person develops paralytic polio, the symptoms are more serious. As the virus spreads through the nerves, it destroys nerves that control muscles. The infection may be fatal if the brain and respiratory organs become affected.