Although polio can cause paralysis and death, the majority of people who are infected with the virus don't get sick and aren't aware they've been infected.

Some people who develop symptoms from the poliovirus contract a type of polio that doesn't lead to paralysis (abortive polio). This usually causes the same mild, flu-like signs and symptoms typical of other viral illnesses.

Signs and symptoms, which can last up to 10 days, include:

• Fever
• Sore throat
• Headache
• Vomiting
• Fatigue
• Back pain or stiffness
• Neck pain or stiffness
• Pain or stiffness in the arms or legs
• Muscle weakness or tenderness

Paralytic polio

This most serious form of the disease is rare. Initial signs and symptoms of paralytic polio, such as fever and headache, often mimic those of nonparalytic polio. Within a week, however, other signs and symptoms appear, including:

• Loss of reflexes
• Severe muscle aches or weakness
• Loose and floppy limbs (flaccid paralysis)

Post-polio syndrome

Post-polio syndrome is a cluster of disabling signs and symptoms that affect some people years after having polio. Common signs and symptoms include:

• Progressive muscle or joint weakness and pain
• Fatigue
• Muscle wasting (atrophy)
• Breathing or swallowing problems
• Sleep-related breathing disorders, such as sleep apnea
• Decreased tolerance of cold temperatures

Poliovirus can be transmitted through direct contact with someone infected with the virus or, less commonly, through contaminated food and water. People carrying the poliovirus can spread the virus for weeks in their feces. People who have the virus but don't have symptoms can pass the virus to others.

Polio mainly affects children younger than 5. However, anyone who hasn't been vaccinated is at risk of developing the disease.

Paralytic polio can lead to temporary or permanent muscle paralysis, disability, bone deformities and death.