Polio: Complete Guide to Symptoms, Causes, and Prevention
Updated: 2 days ago
Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: September 2026
Polio is a viral illness caused by the poliovirus that mainly affects nerves in the spinal cord or brain stem. Most people infected never develop symptoms, but about 5% get mild abortive polio and about 1% get nonparalytic polio. Rarely, the disease progresses to paralytic polio, which can cause permanent paralysis, breathing problems, and sometimes death. There is no cure, so prevention through vaccination is essential, and the worldwide vaccination effort has reduced cases to only a small number in recent years.
Polio, also called poliomyelitis, is an illness caused by the poliovirus that mainly affects nerves in the spinal cord or brain stem. Most people infected don't get symptoms, but the disease can progress to paralytic polio, which can cause limp paralysis — most often of one leg — trouble breathing, and sometimes death. There is no cure, so treatment focuses on comfort and preventing complications. The most effective prevention is vaccination: four doses of inactivated poliovirus vaccine (IPV) in childhood, plus a one-time booster for vaccinated adults traveling to areas where polio is spreading.
What Is Polio?
Polio is an illness caused by a virus that mainly affects nerves in the spinal cord or brain stem. In its most severe form, polio can lead to a person being unable to move certain limbs, also called paralysis. It can also lead to trouble breathing and sometimes death. The disease also is called poliomyelitis.
A vaccination effort throughout the world has led to only a small number of cases occurring around the world in recent years. But poliovirus still spreads within areas with low vaccination rates.
Countries at a higher risk of polio are generally in Africa, the Middle East, and southern and central Asia. Travel notices identifying these areas are published publicly. Vaccinated adults who plan to travel to an area where polio is spreading should get a booster dose of inactivated poliovirus vaccine (IPV). Immunity after a booster lasts a lifetime.
What Are the Symptoms of Polio?
Most people infected with the virus that causes polio, called poliovirus, don't get symptoms. When symptoms do appear, they take one of three main forms.
Form of Polio | How Common | Key Symptoms |
Abortive polio | About 5% of people with the poliovirus | A mild version of the disease with flu-like symptoms lasting 2 to 3 days: fever, headache, muscle aches, sore throat, stomachache, loss of appetite, nausea, vomiting |
Nonparalytic polio | About 1% of those infected | More-severe flu-like symptoms that last longer than a few days, plus neck pain or stiffness, aches or stiffness in the arms or legs, and severe headache. A second phase may follow: stiffness of the spine and neck, decreased reflexes, and muscle weakness |
Paralytic polio | Rare — the most serious form | Begins like nonparalytic polio but progresses to intense pain, extreme sensitivity to touch, tingling or pricking sensations, muscle spasms or twitching, and muscle weakness progressing to a limp paralysis |
What Happens in Paralytic Polio?
Paralytic polio is the most serious form of the disease, and it is rare. The disease begins much like nonparalytic polio but progresses to more-severe signs and symptoms.
Any combination of limbs may experience paralysis. But paralysis of one leg is most common, followed by paralysis of one arm. Depending on the severity of disease, other signs or symptoms may include paralysis of muscles involved in breathing and difficulty swallowing.
What Is Post-Polio Syndrome?
Post-polio syndrome is the appearance of new signs or symptoms or the progression of problems. This usually happens decades after having polio. Common signs and symptoms include progressive muscle or joint weakness and pain, fatigue, muscle wasting, breathing or swallowing problems, sleep-related breathing disorders such as sleep apnea, and lowered tolerance of cold temperatures.
If you had polio before, see your health care provider if you have new or worse signs or symptoms.
What Causes Polio and How Does It Spread?
Polio is caused by the poliovirus. It mainly targets nerve cells in the spinal cord and brain stem that control muscle movement. Nerve cells controlling sensation are generally not affected.
The naturally occurring poliovirus, called the wild-type poliovirus, has been eliminated in most countries and causes few cases of polio. Another version of the virus, called the vaccine-derived poliovirus (VDPV), is more widespread and now causes most infections worldwide.
VDPV exists mainly in a few countries that use an oral vaccine with a weakened poliovirus. The weakened virus in the oral vaccine doesn't itself cause polio, and vaccinated people rarely contract VDPV. Instead, VDPV is a new version of the virus that develops within a community or region where not enough people are vaccinated. Even though the weakened virus doesn't cause illness, it can spread. If most people in a community are vaccinated, the spread of the weakened virus is controlled. If many people aren't vaccinated, the weakened virus can move through a community for a long time, giving the virus the chance to change, or mutate, and behave like the wild-type virus that causes illness.
Infections from VDPV have been reported in the United States. In each case, the person was either not vaccinated or had a significantly weakened immune system. One case in New York in 2022 was in a county with a lower-than-average polio vaccination rate. Samples from wastewater showed that VDPV was spreading in some communities. Since 2000, polio vaccination in the United States has used an injected vaccine with an inactivated poliovirus that doesn't create the risk for VDPV.
People carrying the poliovirus — even people who don't get sick — can pass along the virus in feces, also called stool, or droplets from sneezing or coughing. The virus enters another person through the mouth. The virus can spread easily; for example, it can spread if people haven't washed their hands after coughing, using the toilet, or before eating. The virus also may be in water contaminated with feces carrying the poliovirus.
Polio mainly affects children. But anyone who hasn't been vaccinated is at risk of getting the disease.
What Are the Complications of Polio?
Severe disease that affects the ability to breathe can cause death. Long-term complications for people who recover may include permanent paralysis, muscle shortening that causes deformed bones or joints, chronic pain, and post-polio syndrome.
Complication | Description |
Death | Severe disease that affects the ability to breathe can cause death. |
Permanent paralysis | Limbs may remain unable to move after recovery. |
Muscle shortening | Muscle shortening can cause deformed bones or joints. |
Chronic pain | Ongoing pain can follow the illness. |
Post-polio syndrome | New or worsening symptoms, usually decades after having polio. |
How Can Polio Be Prevented?
The most effective way to prevent polio is vaccination. The recommended schedule calls for four doses of inactivated poliovirus vaccine (IPV) at 2 months, 4 months, between 6 and 18 months, and between ages 4 and 6 when children are just entering school. If your child is missing a dose, talk to your health care provider about a catch-up schedule for vaccination.
In the U.S., most adults have immunity to the poliovirus because of childhood vaccination, and U.S. adults have little chance of being exposed to the virus. But adults who are traveling to or living in a region with high rates of spreading poliovirus should receive more vaccinations. If you had a complete course of vaccination, you should get a one-time IPV booster. You should get three IPV doses if you aren't vaccinated, didn't receive a complete vaccination, or are unsure of your vaccination status. The IPV schedule for adults places a second dose 1 to 2 months after the first dose, and the third dose 6 to 12 months after the second dose. Talk to your health care provider if you know you have an incomplete vaccination history.
IPV is safe for people with weakened immune systems, although it's not certain how protective the vaccine is in cases of severe immune deficiency. Common side effects are pain and redness at the injection site.
IPV can cause an allergic reaction in some people, because the vaccine has trace amounts of the antibiotics streptomycin, polymyxin B, and neomycin. A person who has a severe reaction to a first dose of IPV won't get more doses. Signs and symptoms of an allergic reaction usually occur within minutes to a few hours after the shot and can include skin reactions such as hives, itching, and flushed or pale skin; low blood pressure; narrowing of the airways and a swollen tongue or throat causing wheezing and trouble breathing; a weak and fast pulse; nausea, vomiting, or diarrhea; and dizziness or fainting. Get medical help right away if you or your child has an allergic reaction after any vaccination.
How Is Polio Diagnosed?
Health care providers often recognize polio by symptoms, such as neck and back stiffness or abnormal reflexes or muscle weakness. To confirm the diagnosis, a lab test of a stool sample can detect the poliovirus. The virus can be found in a throat sample only during the first week of illness, so a throat sample is a less reliable source for testing.
A test of the fluid surrounding the brain and spinal cord, or cerebrospinal fluid, may be used to rule out other diseases of the nervous system.
How Is Polio Treated?
Because no cure for polio exists, the focus is on increasing comfort, speeding recovery, and preventing complications. Depending on the severity of disease, supportive treatments may include bed rest, pain relievers, hot moist packs to control muscle pain and spasms, portable ventilators to help with breathing, physical therapy exercises to prevent bone deformity and loss of muscle function, and splints or other devices to encourage good position, or alignment, of the spine and limbs.
Supportive Treatment | Purpose |
Bed rest | Increases comfort and supports recovery. |
Pain relievers | Manages pain. |
Hot moist packs | Controls muscle pain and spasms. |
Portable ventilators | Helps with breathing. |
Physical therapy exercises | Prevents bone deformity and loss of muscle function. |
Splints or other devices | Encourages good position, or alignment, of the spine and limbs. |
When Should You See a Doctor?
Signs and symptoms of polio are similar to other viral diseases that affect the nervous system. It's important to get a timely and accurate diagnosis. The signs and symptoms of moderate to severe polio — beyond typical flu-like symptoms — need attention right away.
If you're preparing for an appointment, be ready to answer questions such as: When did the symptoms begin? Have the symptoms progressed or changed since you first became ill? Has anything improved or worsened the symptoms? Have you traveled recently, and where? Do you know of any possible exposure to an infectious disease? If you traveled, what vaccinations did you get before travel?
Conclusion
Polio is a viral illness that attacks the nerves in the spinal cord or brain stem. Most infections cause no symptoms at all, but in rare cases the disease progresses to paralytic polio, which can cause permanent paralysis, breathing failure, and death. Because no cure exists, treatment is supportive, and vaccination remains the most effective form of prevention. The global vaccination effort has brought polio to only a small number of cases worldwide, though the virus still circulates in areas with low vaccination rates — including rare vaccine-derived cases in the United States.
Next step: Make sure you and your children are up to date on the four-dose IPV schedule. If you're traveling to an area where polio is spreading, check current travel notices and talk to your health care provider about a booster before you go. If you had polio decades ago and notice new or worsening weakness, fatigue, or breathing problems, schedule an evaluation for possible post-polio syndrome.
Frequently Asked Questions (FAQ)
What is polio?
Polio, also called poliomyelitis, is an illness caused by the poliovirus that mainly affects nerves in the spinal cord or brain stem. In its most severe form it can cause paralysis, trouble breathing, and sometimes death.
What are the different forms of polio?
Most people infected don't get symptoms. About 5% develop abortive polio — a mild flu-like illness lasting 2 to 3 days. About 1% develop nonparalytic polio, with neck stiffness, severe headache, and muscle weakness. Rarely, the disease progresses to paralytic polio, which causes limp paralysis and may affect breathing.
How is polio transmitted?
Poliovirus spreads through stool, droplets from sneezing or coughing, unwashed hands, and contaminated water. The virus enters another person through the mouth, and people can spread it even if they never get sick.
Is polio still around?
Cases have dropped to only a small number worldwide thanks to vaccination, but the virus still spreads in areas with low vaccination rates, mostly in Africa, the Middle East, and southern and central Asia. The vaccine-derived poliovirus now causes most infections worldwide.
What is vaccine-derived poliovirus (VDPV)?
VDPV is a mutated version of the weakened virus used in the oral polio vaccine. It develops in communities where too few people are vaccinated, allowing the weakened virus to spread and mutate until it behaves like the wild-type virus that causes illness. It now causes most polio infections worldwide.
What is the polio vaccine schedule?
Four doses of inactivated poliovirus vaccine (IPV) are recommended at 2 months, 4 months, between 6 and 18 months, and between ages 4 and 6. Adults traveling to areas where polio spreads should get a one-time booster; those with no or incomplete vaccination should get three doses.
Is there a cure for polio?
No cure for polio exists. Treatment focuses on comfort, recovery, and preventing complications through bed rest, pain relievers, hot moist packs, ventilators, physical therapy, and splints.
What is post-polio syndrome?
Post-polio syndrome is the appearance of new signs or symptoms, usually decades after having polio. Common symptoms include progressive muscle or joint weakness and pain, fatigue, muscle wasting, breathing or swallowing problems, and sleep apnea.
References and Further Reading
Primary clinical sources: Polio — Symptoms & Causes overview; Polio — Diagnosis & Treatment overview.
Related internal reading:
External references (official sources):
Editorial note: This article is for educational purposes only and does not replace professional medical advice. Always consult a qualified healthcare professional for diagnosis, vaccination decisions, and treatment. Content based on current clinical guidance and published medical sources; reviewed August 2026.
Health information, not medical advice. This article is for general education and is not a substitute for professional diagnosis or treatment. Always consult a qualified healthcare provider about your own health, and seek emergency care for urgent symptoms.
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