Paralytic poliomyelitis, or polio, is a disease that can attack the motor nerves in the spinal cord, leaving the legs or arms paralyzed. In the most severe cases, the muscles of the respiratory system and throat are affected, impairing speech, swallowing and breathing. Because of its propensity to affect infants, the disease came to be known as infantile paralysis.
By some estimates, the incidence of polio dates back 5,000 years, yet it was not until 1909 that a virus was identified as its cause. This important discovery coincided with improvements in sanitation, which paradoxically gave rise to a devastating polio epidemic in 1916. In the United States, young children became paralyzed, and the country was horrified. Previously, babies became naturally immune by acquiring early, mild infections. And antibodies passed from their mothers stimulated life-long immunity. But with greater emphasis on daily bathing and incessant cleanliness, babies were no longer exposed to the virus, which was usually spread by fecal contact. As children, exposure to polio made them susceptible to the most severe infection.
Following the 1916 epidemic, outbreaks occurred in increasing number, gradually affecting older children and young adults. Each summer brought the fear of another polio outbreak. The incidence of polio in the United States rose steadily, with a marked increase in the 1940s. Swimming pools, movie theaters, beaches and other public places closed throughout the country in fearful reaction to the disease. Hospital wards were filled with iron lungs that provided artificial respiration to those not able to breathe on their own. Tens of thousands were treated for polio, and many needed to be fitted with leg braces. As the virus continued to take its toll, President Franklin D. Roosevelt, himself a wheelchair-bound polio victim, in 1938 created the National Foundation for Infantile Paralysis, known today as the March of Dimes, to support care and treatment of polio victims and scientific research aimed at prevention and cure of the disease. Roosevelt’s former law partner, Basil O’Connor, was selected to lead the effort.
Among the first and most important contributions toward prevention were those made by Dr. William Hammon, inaugural chairman of the Department of Epidemiology and Microbiology at the University of Pittsburgh Graduate School of Public Health. In 1949, he had hypothesized that passive immunization – more specifically, injection of blood gamma globulins with antibodies against polio – would temporarily halt infection, prevent clinical disease and confer life-long immunity. Leading the first large double-blind, placebo-controlled clinical trials ever to be conducted, Hammon in 1951 and 1952 enrolled 54,722 children from Provo, Utah; Houston; and Sioux City, Iowa, and provided the first evidence that antibodies to polio could prevent disease. The approach eventually was deemed not practical for widespread use, due in large part to the limited supply of blood plasma.
The major breakthrough came with the development of a vaccine by another University of Pittsburgh group – the research team led by Dr. Jonas Salk. The vaccine made use of an inactivated, or killed, virus and was given by injection to more than 7,500 Pittsburgh-area residents, mostly children, between 1952 and early 1954. These pilot trials provided important evidence on the vaccine’s safety and effectiveness and paved the way for a large-scale trial involving more than 1.8 million children. On April 12, 1955, Dr. Thomas Francis of the University of Michigan, who led the massive national trial, pronounced the vaccine effective, news that gave hope that polio could be conquered.
Between 1955 and 1957, when the Salk vaccine was widely used, the incidence of polio in the United States fell by 85 to 90 percent, with only 15,000 cases reported in 1956. By 1962, when an oral live poliovirus vaccine developed by Albert Sabin succeeded the Salk vaccine, the incidence of polio had decreased by 95 percent. Eventually, the development of the two polio vaccines eradicated naturally occurring poliomyelitis in North America, South America and Western Europe.
Because of the small risk that the live vaccine could cause polio in those receiving it and their close contacts, the U.S. Department of Health and Human Services in 1999 recommended the routine use of the Sabin vaccine be discontinued in favor of the killed poliovirus vaccine that had originally been developed at the University of Pittsburgh. The Sabin vaccine continues to be used by the World Health Organization in its Global Eradication Initiative, a campaign especially targeted in those African and Asian countries where cases of polio remain a threat.
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