Questions & Answers

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What causes polio?
Polio is caused by a virus.

How does polio spread?
Polio is usually spread via the fecal-oral route (i.e., the virus is transmitted from the stool of an infected person to the mouth of another person from contaminated hands or such objects as eating utensils). Some cases may be spread directly via an oral to oral route.

How long does it take to show signs of polio after being exposed?
The incubation period for polio is commonly 6-20 days, with a range of 3-35 days.

What are the symptoms of polio?
Surprisingly, 95% of all individuals infected with polio have no apparent symptoms.

Another 4%-8% of infected individuals have symptoms of a minor, non-specific nature, such as sore throat and fever, nausea, vomiting, and other common symptoms of any viral illness.

About 1%-2% of infected individuals develop nonparalytic aseptic (viral) meningitis, with temporary stiffness of the neck, back, and/or legs. Less than 1% of all polio infections result in the classic "flaccid paralysis," where the patient is left with permanent weakness or paralysis of legs, arms, or both.

How serious is polio?
Although most cases of polio are mild, the 1% of cases resulting in flaccid paralysis have made polio a feared disease for hundreds of years. Of persons with paralytic polio, about 2%-5% of children die and up to 15%-30% of adults die.

Are there any long-term concerns for persons who contracted paralytic polio in childhood?
It has been discovered that about 25%-40% of persons who suffered from paralytic polio as a child develop new symptoms in adulthood (usually after an interval of 30-40 years). This problem is called post-polio syndrome (PPS) and symptoms can include new muscle pain, weakness, or paralysis. PPS is not infectious. For more information or for support for persons with post-polio syndrome, go to: www.post-polio.org

How is polio diagnosed?
If a person is suspected of being infected, a sample from their stool or throat should be tested for the poliomyelitis virus.

How long is a person with polio contagious?
Patients infected with the polio virus can pass the virus on for 7-10 days before the onset of disease. In addition, they can continue to shed the virus in their stool for 3-6 weeks.

Is there a treatment for polio?
There is no "cure" for polio. Persons infected with polio need supportive therapy, such as bed rest and fluids. Standard precautions should be taken to avoid passing on the virus through any contamination from the patient's stool.

How common is polio in the U.S.?
Before a polio vaccine was developed, polio epidemics were common in the United States. For example, in the immediate pre-vaccine era (i.e., early 1950s), between 13,000 and 20,000 paralytic cases were reported each year. After the development of the inactivated (Salk) injectable vaccine in 1955 and the live (Sabin) oral vaccine in 1961, the number of polio cases dropped dramatically. In 1960, there were 2,525 paralytic cases reported, but by 1965 this number had fallen to 61.

Due to a concentrated effort to eradicate polio from the world, there have been no cases of "wild" (i.e., natural) polio acquired in the United States since 1979, and no cases of wild polio acquired in the entire Western Hemisphere since 1991.

How common is polio in the world?
In 1988, the World Health Organization (WHO) adopted the goal of global polio eradication. Although the initial target date of 2000 was not met, substantial progress has been made. In 1988, there were estimated to be 350,000 reported cases of polio in the world; in 2001, just 483 cases were reported. Unfortunately, rumors about the safety of polio vaccine in 2003, and subsequent refusal of vaccine by many parents in Nigeria, led to an increase in cases and spread of the virus to nearby countries that had previously been polio free. In 2003, there were 784 reported cases; in 2004, there were 1,255 reported cases.

Wild polio currently exists only in a few countries in Asia and Africa. In 2008, there were 1,659 cases of polio in 18 countries, according to the Global Polio Eradication Initiative. Many organizations have been working hard toward eradicating polio including WHO, the United Nations Children's Fund (UNICEF), the Centers for Disease Control and Prevention (CDC), Rotary International, the Bill and Melinda Gates Foundation, and many other international and national groups. Strategies include house-to-house vaccination and National Immunization Days, where even warring factions have called temporary cease fires to allow children to be vaccinated.

Questions and answers about polio vaccine

Technically reviewed by the Centers for Disease Control and Prevention, April 2009