About 1 to 2 percent of infected people will develop aseptic meningitis from poliovirus. For these people, early symptoms can be similar to minor polio symptoms. Then aseptic meningitis symptoms can develop, including stiffness of the back or legs and increased or abnormal sensations. These symptoms improve rapidly, usually within a couple of days (2-10 days) with complete recovery.
Less than 1 percent of polio cases will result in paralysis. In these severe cases, symptoms begin with:
- Muscle aches
- Loss of reflexes
- Other "minor illness" symptoms.
These early symptoms improve after several days. However, 5 to 10 days later, the fever returns and paralysis begins. Paralysis progresses for two to three days. Once the temperature returns to normal, there is usually no further paralysis. Along with paralysis, other polio symptoms with paralytic poliomyelitis can include painful muscle cramps and muscle twitching.
The risk of paralysis with polio increases with age. In children under the age of five, paralysis of one leg is common. In adults, paralysis of both arms and legs is common. The muscles that control urination and breathing may also be affected.
Many people with paralytic poliomyelitis recover completely, and muscle function returns to some degree. However, paralysis after six months is usually permanent.
People who develop serious symptoms (including paralysis) may experience complications. Polio complications in severe cases can include:
About 2 to 5 percent of children and 15 to 30 percent of adults with paralytic polio die from the poliovirus infection.