Polio Disease - Questions and Answers
What is Polio?
Polio is an infectious disease caused by a virus that lives in the throat and intestinal tract. It is most often spread through person-to-person contact with the stool of an infected person and may also be spread through oral/nasal secretions. 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, however for the less than 1% who develops paralysis it may result in permanent disability and even death.
What are the symptoms of polio?
Up to about 72% of susceptible persons infected with polio have no symptoms. However, infected persons without symptoms can still spread the virus and cause others to develop polio. About 24% of infected susceptible persons have minor symptoms such as fever, sore throat, upset stomach, or flu-like symptoms and have no paralysis or other serious symptoms. About 1-5% develop aseptic meningitis with stiffness of the back, back, or legs, and in some persons increased or abnormal sensations a few days after the minor illness resolves. These symptoms typically last from two to ten days, followed by complete recovery. Less than 1% of polio cases result in paralysis of the limbs (usually the legs). Of those cases resulting in paralysis, 5-10% of the patients die when the respiratory muscles are paralyzed. 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. Periodic epidemics occurred since the late 19th century and they increase in size and frequency in the late 1940s and early 1950s. An average of over 35,000 cases were reported during this time period. With the introduction of Salk inactivated poliovirus vaccine (IPV) in 1955, the number of cases rapidly declined to under 2,500 cases in 1957. By 1965, only 61 cases of paralytic polio were reported.
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 162 confirmed cases of paralytic polio cases reported. Of the 162 cases, eight cases were acquired outside the United States and imported. The last imported case caused by wild poliovirus into the United States was reported in 1993. The remaining 154 cases were vaccine-associated paralytic polio (VAPP) caused by live oral poliovirus vaccine (OPV).
What kind of polio vaccines are used in the United States?
IPV, which is given as a shot, is now used in the United States. OPV has not been used in the United States since 2000 but is still used in many parts of the world.
What is a vaccine-derived poliovirus?
A vaccine-derived poliovirus (VDPV) is a strain of poliovirus that was initially contained in OPV and that has changed over time and behaves more like the 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 VDPV and one cause by wild poliovirus or OPV?
No, there is no clinical difference between paralytic polio caused by wild poliovirus, OPV, or VDPV.
I've heard that VDPV has been found recently in the United States. Is this true?
In 2005, a VDPV was found in the stool of an unvaccinated, immunocompromised 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 2 months prior. Subsequently, seven other unvaccinated children in the the child's community were shown to have poliovirus infection. None of the infected children had paralysis. For more information specifically related to this case, visit http://jid.oxfordjournals.org/content/199/3/391.full.pdf In 2009, an immunoncompromised adult developed vaccine-associated paralytic polio (VAPP) and died of polio-associated complications. VDPV was isolated, and the infection likely occurred where her child received OPV 12 years prior.
Where do vaccine-derived polioviruses come from, and should I be concerned if there is a case in the United States?
VDPVs can cause outbreaks in countries where vaccine coverage with OPV is low. Long-term excretion can also occur in people with certain immunodeficiency disorders. Because OPV has not been used in the United States since 2000 and vaccine coverage with IPV is high, it is unlikely that any vaccine-derived poliovirus (VDPV) seen in the United States would become widespread.
Also, polio vaccination protects people against naturally occurring polioviruses and vaccine-derived polioviruses.
Who should get polio vaccine and when
The poliovirus vaccine used in the United States is IPV. 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.
IPV is routinely given to children. Children get 4 doses 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
For more information on routine poliovirus vaccine schedules, please see the childhood, adolescent, and catch-up schedules.
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