Merck Manual

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The Manual's Editorial Staff

Last full review/revision Mar 2020| Content last modified Mar 2020
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What is polio?

What causes polio?

Polio is caused by the poliovirus. It's very contagious and is spread by contact with infected people.

Polio was common in much of the world until the 1950s, when a vaccine became available. The last case of polio in the United States was in 1979. People still get polio in parts of Africa (especially Nigeria), Pakistan, and Afghanistan.

What are the symptoms of polio?

Most people don’t have any symptoms. If you do have symptoms, they usually are mild, such as fever, sore throat, and mild headache. Because people aren't very sick, doctors don't usually do any tests and the illness isn't even recognized as polio.

A few people have more serious symptoms:

  • Very bad headache

  • Stiff neck and back

  • Muscle pain

Some of the people with more serious symptoms have worse problems:

  • Muscle weakness that may be long-lasting

  • Paralysis, making you unable to move part of your body

The paralysis can affect different parts of your body. You may be unable to move one or both legs. You may be unable to swallow or even breathe.

How can doctors tell if I have polio?

Doctors suspect polio based on your symptoms and whether you have been in an area where other people have polio. To tell for sure, they’ll:

How do doctors treat polio?

There's no cure for polio. Doctors will:

People with mild cases of polio usually recover completely. People with severe polio usually have long-lasting muscle weakness. Sometimes, even if symptoms get better or go away, the muscle weakness can get worse or return many years later (postpolio syndrome).

How can I prevent polio?

  • In the United States, children get a shot at 2 months, 4 months, 6 to 18 months, and 4 to 6 years

  • If you’re traveling to an area where there’s polio, talk to your doctor about whether you need another shot even if you've had one before

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