Although the most visible sign of polio infection polio paralysis, fewer than 1% of polio infections ever result in paralysis. Most cases produce very mild or no symptoms and usually go unrecognized. A further 5% to 10% of polio infections result in aseptic meningitis, a viral inflammation of the outer covering (meninges) of the brain. The rest involve mild flu-like symptoms common to other viral infections – mild fever, sore throat, abdominal pain, and vomiting.
No one knows why only a small percentage of infections lead to paralysis. Several key risk factors have been identified as increasing the likelihood of paralysis in a person infected with polio. These include:
• Immune deficiency
• Pregnancy
• Removal of the tonsils (tonsillectomy)
• Intramuscular injections
• Strenuous exercise
• Injury
