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Diseases > Polio
FAQs (frequently a
sked questions)
about Polio

Contents of this page:
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General questions 

What is Polio?

Polio is an infectious disease caused by a virus that lives in the throat and intestinal tract. It is spread through person-to-person contact with the stool of an infected person (for instance, by changing diapers). Polio used to be very common in the U.S. and caused severe illness in thousands of people each year before polio vaccine was introduced in 1955.

Most people infected with the polio virus have no symptoms but some infections cause paralysis and even death.

What are the symptoms of polio?

Up to about 95 percent of people infected with polio have no symptoms. However, infected persons without symptoms can still spread the virus and cause others to develop polio. About four to eight percent of infected persons have minor symptoms such as fever, sore throat, upset stomach, or flu-like symptoms and have no paralysis or other serious symptoms. About one to two percent of infected persons develop aseptic meningitis with stiffness of the back, back or legs, and in some persons increased or abnormal sensations. Symptoms typically last from two to ten days, followed by complete recovery. Less than 1 percent of polio cases result in paralysis. The risk of paralysis increases with age.



How common was polio in the United States?

Polio was one of the most dreaded childhood diseases of the 20th Century in the United States. There were usually about 13,000 to 20,000 cases of paralytic polio reported each year in the US before the introduction of Salk polio vaccine in 1955. Polio peaked in 1952 when there were more than 21,000 reported cases. The number of cases of polio decreased dramatically following introduction of the vaccine and the development of a national vaccination program. In 1965, only 61 cases of paralytic polio were reported compared to 2,525 cases reported cases just five years earlier in 1960.


Is polio still a disease seen in the United States? 

The last cases of naturally occurring paralytic polio in the United States were in 1979, when an outbreak occurred among the Amish in several Midwestern states. From 1980 through 1999, there were 152 confirmed cases of paralytic polio cases reported. Of the 152 cases, eight cases were acquired outside the United States and imported. The last imported case caused by wild poliovirus into the Untied States was reported in 1993. The remaining 144 cases were vaccine-associated paralytic polio (VAPP) caused by live oral polio vaccine. 

What kind of polio vaccines are used in the United States?

Only one kind of polio vaccine, IPV, which is given as a shot, is now used in the United States.  A live, oral polio vaccine (OPV) has not been used in the United States since 2000 but is still used in many parts of the world.


Vaccine-derived poliovirus related questions

What is a vaccine-derived poliovirus?

A vaccine-derived poliovirus (VDPV) is a strain of polio virus, initially contained in the live OPV, that has changed over time and behaves more like a wild or naturally-occurring virus. This means it can be more easily spread to others who are unvaccinated against polio and who come in contact with the stool or oral secretions (e.g. saliva) of an infected person. These viruses may cause illness, including paralytic poliomyelitis.

Is there a difference in a disease caused by a VPDV and one cause by wild poliovirus or OPV?

No, there is no clinical difference between paralytic polio caused by wild poliovirus, OPV or a VDPV.

I’ve heard that a child has been found with VDPV. Is this true?

In 2005, a VDPV was found in the stool of an unvaccinated child in the state of Minnesota. The child most likely caught the virus through contact in the community with someone who received live oral vaccine in another country. For questions specifically related to this case visit


Where do vaccine-derived polioviruses come from?

Because OPV has not been used in the United States since 2000, it is likely that any vaccine-derived poliovirus (VDPV) seen in the United States would have come from a person who received OPV in another country. OPV is used in many countries of the world, including Central and South America, Africa, and Asia.

Should I be concerned if there is a case of VDPV in the United States?

Polio vaccination can protect people against naturally occurring polioviruses and vaccine-derived polioviruses. It is unlikely that a VDPV would become widespread because most people in the United States have been vaccinated against polio. Most VDPVs disappear over time without causing any clinical disease. Very rarely, usually in communities where routine polio immunization has been low, VDPVs have spread beyond close contacts. Over the past decade, more than ten billion doses of OPV have been given worldwide, with only 6 outbreaks of circulating VDPVs confirmed, resulting in only approximately 50 cases of paralytic polio. Persons who are not up to date with polio immunizations should talk with their healthcare provider.


Vaccine related questions

Who should get polio vaccine and when?

Polio vaccine or IPV is a shot, given in the leg or arm, depending on age. Polio vaccine may be given at the same time as other vaccines.

Most people should get polio vaccine when they are children. Children get 4 doses of IPV, at these ages:

  • A dose at 2 months
  • A dose at 4 months
  • A dose at 6-18 months
  • A booster dose at 4-6 years

Most adults do not need polio vaccine because they were vaccinated as children. But, in general, three groups of adults are at higher risk for coming into contact with polio virus and should consider polio vaccination:

  • people traveling to areas of the world where polio is common,
  • laboratory workers who might handle polio virus, and
  • health care workers treating patients who could have polio.

Adults in these three groups as well as those in communities where VPDV has been isolated who have never been vaccinated against polio should get 3 doses of IPV:

  • The first dose at any time,
  • The second dose 1 to 2 months later,
  • The third dose 6 to 12 months after the second.

As accelerated vaccination schedule can be used for unvaccinated children and adults with 4 week intervals between the 3 doses of the primary series.

Adults at high risk of coming in contact with polio virus who have received the 3 dose primary series should receive a booster dose of IPV. Based on available information, adults do not need more than a single lifetime booster dose with IPV.

Ask your health care provider for more information. Recommendations for polio vaccine in the United States are available at: or


How many children are vaccinated against polio in the United States?

According to the 2004 National Immunization Survey conducted by the Centers for Disease Control and Prevention (CDC), about 92 percent of children aged 19 to 35 months living in the United States were vaccinated against polio. About 95.5 percent of US children are vaccinated against polio before school entry.


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This page last modified on October 4, 2005


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