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What Is Polio?

Polio (also called poliomyelitis) is a contagious, historically devastating disease. It was virtually eliminated from the Western hemisphere in the second half of the 20th century. Although polio has been around since ancient times, its largest outbreak was in the first half of the 1900s until the polio vaccine was introduced in 1955.

What Are the Signs & Symptoms of Polio?

Polio is a viral illness that in most cases causes no symptoms (called asymptomatic polio). When there are symptoms (symptomatic polio), the illness appears in three forms:

  1. a mild form called abortive polio: Most people with this type may not suspect they have it because their sickness is limited to mild flu-like symptoms such as mild upper respiratory infection, diarrhea, fever, sore throat, and a general feeling of being ill.
  2. a more serious form associated with aseptic meningitis called nonparalytic polio: A few people with this type have symptoms such as sensitivity to light and neck stiffness.
  3. a severe, debilitating form called paralytic polio: This occurs in 0.1%-2% of cases.

People who have abortive polio or nonparalytic polio usually make a full recovery. Paralytic polio, though, causes muscle paralysis and even death.

In paralytic polio, the virus leaves the intestinal tract and enters the bloodstream, attacking the nerves (in abortive or asymptomatic polio, the virus usually doesn't get past the intestinal tract). The virus may affect the nerves controlling the muscles in the limbs and the muscles necessary for breathing, causing respiratory difficulty and paralysis of the arms and legs.


In the United States, it's currently recommended that children have four doses of inactivated polio vaccination (IPV) between the ages of 2 months and 6 years.

By 1964, the oral polio vaccine (OPV) had become the recommended vaccine. OPV allowed large populations to be immunized because it was easy to administer, and it provided "contact" immunization, which means that an unimmunized person who came in contact with a recently immunized child might become immune, too.

The problem with OPV was that, in very rare cases, paralytic polio could develop either in immunized children or in those who came in contact with them. Since 1979 (when wild polio was eliminated in the United States), the approximately 10 cases per year of polio seen in this country were traced to OPV.

IPV is a vaccine that stimulates the immune system of the body (through production of antibodies) to fight the virus if it comes in contact with it. IPV cannot cause polio.

In an effort to eradicate all polio, including those cases associated with the vaccine, the Centers for Disease Control and Prevention (CDC) decided to make IPV the only vaccine given in the United States. Currently, the CDC and American Academy of Pediatrics (AAP) recommend three spaced doses of IPV given before the age of 18 months, and an IPV booster given between the ages of 4 to 6, when children are entering school.

If you're planning to travel outside the United States, particularly to Africa and Asia (where polio still exists), be sure that you and your kids have received a complete set of polio vaccinations.


Although the acute illness usually lasts less than 2 weeks, damage to the nerves could last a lifetime. In the past, some patients with polio never regained full use of their limbs, which would appear withered. Those who did fully recover might go on to develop post-polio syndrome (PPS) as many as 30 to 40 years after contracting polio. In PPS, the damage done to the nerves during the disease causes an acceleration of the normal, gradual weakness due to aging.


During the height of the polio epidemic, the standard treatment involved placing a patient with paralysis of the breathing muscles in an "iron lung" — a large machine that actually pushed and pulled the chest muscles to make them work. The damaged limbs were often kept immobilized because of the confinement of the iron lung. In countries where polio is still a concern, ventilators and some iron lungs are still used.

Historically, home treatment for paralytic polio and abortive polio with neurological symptoms wasn't sufficient. However, asymptomatic and mild cases of abortive polio with no neurological symptoms were usually treated like the flu, with plenty of fluids and bed rest.

The Future of Polio

Health groups are working toward wiping out polio throughout the world, and much progress has been made. But several countries still have polio circulating, which means that the virus could occur in others. If the polio virus reaches a country where not enough people have been immunized, it could spread from person to person, as has happened in some countries in Africa and Asia. So until it has been eliminated worldwide, it's important to continue vaccinating kids against polio.

Reviewed by: Nicole A. Green, MD
Date reviewed: January 2014