Polio (short for poliomyelitis, once called infantile paralysis), used to strike thousands of children in the United States each year. In 1955, it was announced that the Salk vaccine was safe and effective against this disabling, sometimes fatal infection. Due to the Salk vaccine, and soon afterward the Sabin oral vaccine, both developed with March of Dimes funding, wild (not vaccine-associated) polio infections have been eliminated from the United States for nearly 3 decades (1). Polio still occurs, however, in some developing countries.
What is polio?
Polio is a disease that can infect the central nervous system (brain and spinal cord) and cause lasting disabilities in a small number of infected individuals. It is caused by any of three types of polio viruses. Polio infection is most common in infants and children, but young adults and some older people get it, too (2).
Up to 95 percent of individuals with a polio infection have no symptoms (1). A small number (4 to 8 percent) have mild symptoms, such as a sore throat, headache, malaise, upset stomach and low-grade fever (1). These individuals generally recover completely within a week.
However, from the digestive tract (stomach and intestines), the virus can get into the blood stream and be carried to the central nervous system. About 1 to 2 percent of infected individuals develop a high fever, meningitis (inflammation of membranes surrounding the brain and spinal cord), stiff neck and limb pain (1). These individuals generally recover completely, usually within 10 days (1).
In fewer than 1 of every 100 infected persons, the virus attacks nerves inside the spine that send messages to muscles in arms, legs and other areas (1). This can result in partial or complete paralysis. If the virus gets into the brainstem (bulbar polio), muscles needed for breathing, swallowing and other vital functions become paralyzed, and the person may die.
How does polio spread?
The virus is spread from person to person by contact with infected secretions from the nose or mouth or by contact with infected feces. It usually enters the body when the person ingests contaminated food or water or touches the mouth with contaminated hands.
How is polio treated?
There is no drug that can cure polio once a person is infected. Individuals are made as comfortable as possible, with bed rest, pain-relieving medications and hot packs to help relieve the pain of extreme muscle tightness. Some need assistance with breathing, such as supplemental oxygen or a ventilator.
During the epidemics of the 1930s, 1940s and 1950s, some patients with serious breathing problems were placed in an "iron lung," a cylindrical chamber that surrounded a patient's body from the neck down, which used rhythmic alterations in air pressure to force air in and out of the individual's lungs.
After the active stage of the disease is over, surviving nerve cells gradually send out new nerve connections to orphaned muscle cells in an attempt to take over the function of nerve cells that were destroyed. This often allows the patient to regain use of muscles and recover, partially or completely. Patients with permanent, partial paralysis are taught to use remaining healthy muscles. They generally go on to lead active lives, although some require braces and wheelchairs.
How is polio prevented?
Polio is prevented by vaccination. There are two types of polio vaccine; one is injected (a shot) and one is given by mouth.
The Salk vaccine (the first to be approved, in 1955) is made from completely inactivated polio viruses and injected into the body.
The oral vaccine (known as the Sabin vaccine) is made from weakened polio viruses. It was introduced in 1963.
Both vaccines cause the body to produce antibodies, which are specialized proteins produced by the immune system that fight the polio viruses. The vaccines make a person immune to polio. (Immune means that a person is protected from an infection and cannot get it.) The vaccines immunize against all three virus types.
Children in the United States are routinely vaccinated against polio, along with other preventable diseases. They receive four doses of the vaccine at 2, 4, 6 to 18 months and 4 to 6 years (1).
Until the late 1990s, the polio vaccine usually was given by mouth. Very rarely, paralytic polio occurs in children who have been vaccinated with the oral vaccine or in others with whom they've had contact. About 8 to 10 cases of vaccine-associated paralytic polio occurred each year in the United States in the 1980s and 1990s (1). As of January 2000, the Centers for Disease Control and Prevention (CDC) and the American Academy of Pediatrics recommend that babies in the United States be vaccinated against polio with the shot, which cannot cause polio (1, 2). The oral polio vaccine is no longer routinely available in the United States (1).
Are travelers at risk of contracting polio?
Polio still occurs in certain developing countries, mainly in some parts of Africa and south Asia (3). Due to global efforts to eradicate this disease by vaccinating children, polio cases have decreased by more than 99 percent since 1988, with fewer than 2,000 cases reported worldwide in 2005 (3).
Adults or children who are traveling to less developed countries where polio is still common should check with their health care provider or local health department to see if they need a "booster" dose. Generally, one additional polio shot is recommended for adults who were vaccinated during childhood and are traveling to these areas (1, 2).
Are there late effects of polio?
Yes. Some individuals who had polio when young experience progressive new muscle weakness decades afterward. This weakness can affect muscles previously weakened by polio as well as muscles believed to have been unaffected. These people also sometimes report intense fatigue and pain in muscles and joints. This finding of new weakness, fatigue and pain many years after having polio is called post-polio syndrome (PPS). However, not all polio survivors with such symptoms have PPS. Some, when examined by doctors, are found to have arthritis or other common joint and muscle disorders.
What is the cause of PPS?
Many experts believe that the overburdened nerve cells that sent out new connections to take over for destroyed nerve cells eventually begin to fail, resulting in new muscle weakness (4, 5). Other factors, including normal aging, probably also play a role.
How is PPS diagnosed and treated?
Polio survivors who believe they are having the symptoms of PPS should be thoroughly evaluated by a doctor who is an expert in neuromuscular disorders. Such experts may include physiatrists (rehabilitation specialists), neurologists, orthopedists and others with special training in these disorders. Before such evaluation, individuals should not increase exercise or activity in the hope that this will give their muscles more strength. An increase in physical activity actually might do more damage. The best thing to do is seek expert medical help.
Sometimes a change in braces, a decrease in activity, or treatment of conditions like arthritis will lessen symptoms. Specially designed exercise programs also can help improve strength and functioning.
What is the role of the March of Dimes?
Many people remember the March of Dimes for conquering epidemic polio, and the Foundation continues to receive questions about the disorder. The March of Dimes responds to these inquiries and often refers people to sources of help.
In May 2000, funded by a special donation, the March of Dimes sponsored an international conference on best practices in diagnosis and management of PPS. Findings from the conference have been widely disseminated to patients and health care professionals (4, 6).
Historians have called the conquest of polio one of the great achievements of the 20th century. Thanks to the March of Dimes, and the millions of people who supported the Foundation, we no longer have to fear another devastating polio epidemic like the ones that terrorized previous generations.
- Centers for Disease Control and Prevention (CDC). The Pink Book: Epidemiology and Prevention of Vaccine-Preventable Diseases, 10th Edition, February 2007.
- American Academy of Pediatrics (AAP). Poliovirus Infections, in: Pickering L.K.(ed.) 2006 Red Book: Report of the Committee on Infectious Diseases 27th edition, Elk Grove Village, IL, American Academy of Pediatrics, 2006, pages 542-547.
- World Health Organization. Poliomyelitis Fact Sheet. September 2006.
- March of Dimes Steering Committee on Post-Polio Syndrome. March of Dimes International Conference on Post-Polio Syndrome: Identifying Best Practices in Diagnosis and Care. White Plains, N.Y., 2002.
- National Institute of Neurological Disorders and Stroke. Post-Polio Syndrome Fact Sheet. April 17, 2007.
- March of Dimes. Guidelines for People Who Have Had Polio. White Plains, N.Y., 2002.