Poliomyelitis, or infantile paralysis, is a virus disease affecting the central nervous system. The infection passes from person to person by the fecal-oral route. Throughout most of human history the polio virus was ubiquitous and infected almost all children as soon as they were weaned from breast milk to a mixed diet, but infection caused symptoms in only a small minority. Infants exposed to the polio virus when they were first weaned retained some residual maternal immunity, or else the virus was less virulent before the early twentieth century when the disease began occurring in EPIDEMICS of paralytic poliomyelitis. For either or both of these reasons, the infection usually passed unnoticed since it caused neither symptoms nor signs.

Early History

Poliomyelitis occurs when the virus invades the nervous system and attacks nerves that activate muscle movement, but in many cases infection with the polio virus causes no signs or symptoms at all. The symptoms include fever, headache, and muscle pains, rapidly followed by the onset of localized muscle paralysis, which is permanent. Depending on which nerves are attacked–that is, which muscles are paralyzed– the outcome varies from mild weakness of part of an arm or leg to death if nerves in the brain stem that control muscles required for breathing and swallowing are paralyzed. Until about the 1920s polio was a disease of infants and young children, but older children, adolescents, and adults occasionally got it too. When a limb was paralyzed in childhood, the muscles wasted away and the limb did not continue to develop at the same rate as that on the unaffected side, leading to a shriveled arm or leg or some worse deformity, depending upon the severity of the disease.

We know that poliomyelitis has existed for thousands of years. A stone carving from Egypt, dated about 1500 B.C.E., shows a youth with the deformed shrunken leg that is characteristic of polio and has virtually no other possible cause. The old name for the disease, infantile paralysis, recalls the time when it was primarily a disease of infants and very young children and its outcome was paralysis of the affected muscles. Both the little crippled boy who could not follow the Pied Piper of Hamelin and Tiny Tim in Charles Dickens' classic A Christmas Carol, were probably victims of infantile paralysis. Because of its fecal-oral transmission route and because of ecological factors such as the prevalence of flies to carry fecal contamination to food in summer, poliomyelitis was always predominantly a summertime disease.

Polio Epidemics

When standards of domestic HYGIENE and environmental sanitation began to improve in the rich nations of Europe and North America after the sanitary reforms of the late nineteenth and early twentieth centuries, infants often escaped infection and the disease began to have a greater impact on older children, adolescents, and young adults, and began to occur in epidemics. Repeated epidemics affecting significant numbers of children, adolescents, and young adults became commonplace in North America, Europe, and Australia early in the twentieth century.

These epidemics had dramatic effects on family life and society at a time when INFANT MORTALITY and family size were declining. The life and health of every child seemed more precious to most people than perhaps it had in the days when it was an accepted fact of life that a great many newborn infants did not survive. And it was almost as bad for parents to see their children struck down by a disease that left them crippled as to see them die. Parents sometimes took extraordinary precautions to protect their children. Polio was known to be due to an infectious pathogen but until the 1950s it was not known how this pathogen was transmitted. In the large epidemics of the 1930s and 1940s, schools, cinemas, public swimming pools, and sports arenas were closed, perhaps reinforcing a mood of mass anxiety bordering on hysteria that the size and true impact of these epidemics did not justify. The epidemics were in fact numerically small in comparison to the great epidemics of cholera, typhus, and smallpox of the nineteenth century.

The Medical Response

The medical response was more rational. Special hospital facilities were developed to deal with the care of children and young adults with paralyzed respiratory muscles. Modern intensive-care nursing and specialized intensive care units evolved from the early treatment of severe epidemic poliomyelitis, which was still often called infantile paralysis. Cecil Drinker (1887-1956), an American physiologist, invented a respirator commonly known as an iron lung, in which children with paralyzed respiratory muscles were nursed, often for many months or even years, and their breathing was maintained by means of a pistonlike device that kept air pressure below atmospheric level, expanding the chest as air was sucked into the lungs. The machines, the intensive nursing care that was required with them, the prolonged aftercare with skilled physiotherapy, and appliances to assist paralyzed people to get about, were costly. When Franklin Delano Roosevelt was struck down with severe polio in 1921, the disease and its expensive treatment and aftercare acquired a high public profile. The charitable foundation March of Dimes, founded in 1935, was born in a wave of massive public sympathy for the young victims of infantile paralysis. Unlike other charitable foundations of that time, the March of Dimes relied on innumerable small donations rather than a few large ones, and in this way it was able to raise enough money not only to pay for many of the expensive treatment facilities but also to invest in research.

Research focused partly on improved treatment and rehabilitation methods, but it was much more important to find a way to prevent the disease. This required discovery of the causative organism, epidemiological studies to elucidate the way polio was spread, and development of ways to prevent the spread and immunize infants and children. All these advances were among the achievements of medical science in the first half of the twentieth century. The virus responsible for the infection was discovered in 1908 by the Austrian microbiologist Karl Landsteiner (1868-1943) and the discovery was confirmed in 1910 by Simon Flexner (1863-1946) at the Rockefeller Institute in New York. These discoveries, in the early years of virology, were based on inference as much as on direct observation.

Development of a vaccine to protect against infection could not begin until ways to cultivate the virus artificially were developed. Before this happened, several therapeutic innovations emerged, sometimes with unhappy consequences. Vaccine trials in 1935, using convalescent human serum, may actually have enhanced the risk of paralytic polio and may also have transmitted other virus diseases such as hepatitis. Sister Elizabeth Kenny, an Australian nurse, advocated movement and massage of affected limbs, in contrast to the then-orthodox procedures of immobilization for prolonged periods. Her ideas were theoretically sound but in practice sometimes did more harm than good.

The first important breakthrough on the way to developing polio vaccines was the work by John Enders (1897-1985) and colleagues, who successfully grew the polio virus in tissue cultures in 1949. Jonas Salk (1914-1995) used tissue cultures of polio virus to produce the first successful vaccine that could provide immunological protection against poliomyelitis. The Salk vaccine was tested in the early 1950s and licensed for general use in 1955. The Salk vaccine had to be given by injection and was sensitive to temperature extremes. Albert Sabin (1906-1993) developed a vaccine that used live attenuated polio virus, which could be orally administered as a drop of vaccine on the tongue (or on a sugar lump) and was better able to withstand tropical temperatures; the Sabin vaccine came into general use around 1960 and superceded the Salk vaccine, despite the small (and mostly theoretical) risk that the live virus vaccine might mutate under some circumstances into a more virulent strain that could cause paralytic poliomyelitis.

The use of polio vaccines has virtually eliminated poliomyelitis from much of the world. The disease was declared eradicated from the western hemisphere in 1994. It remains a risk in low-income countries in Africa and Asia and among small groups of people such as members of certain religious sects who for reasons connected with their faith refuse to accept vaccination against poliomyelitis and other diseases.

See also: Contagious Diseases; Vaccination.


Paul, J. R. 1971. A History of Poliomyelitis. New Haven: Yale University Press.

Robbins, F. C. 1999. "The History of Polio Vaccine Development." In Vaccines, 3rd edition, ed. S. A. Plotkin and W. A. Orenstein. Philadelphia: Saunders.

Zuber, P. L. F. 2002. "Poliomyelitis." In Encyclopedia of Public Health, ed. L. Breslow, B. D. Goldstein, L. W. Green, et al., pp. 932-933. New York: Macmillan.