The Continuing History of Poliomyelitis

Infantile Paralysis. This sinister name was given to a disease which was virtually unheard-of before the late 19th century, but which began terrorizing developing countries and swept across the world. Many believe it has existed for centuries. In Trial by Fury: the Polio Vaccine Controversy, Aaron Klein includes a picture of a mural in Egypt which some believe shows an early victim of the disease – a priest with a withered leg.1 Other theories as to its origin abound, but its imprint is undeniable in the histories of Western countries (and eventually the world) throughout the 20th century. This disease is now better known as poliomyelitis.

The long-standing scientific explanation for the sudden spike in polio case levels in the early 1900s states that increased sanitation actually encouraged the spread of the disease. In the “dirtier” days of the past, many were exposed to the virus throughout their lives and they developed immunity to it because they were exposed to small amounts without getting paralytic cases of it2. In addition, some of the mother’s antibodies against polio were passed on to her infant (through breast milk) so that infants were protected during the earliest months of their lives. Since most of the community was immune, when someone did get paralytic polio, it did not spread very far until the chain of immunity was broken in developing countries. As better sanitation practices provided cleaner water, among other things, many in the population were no longer immunized through low-level exposure. Now epidemics arose at alarming rates, particularly during the summer months when more children were likely to be in close proximity to each other (and the virus) for long periods of time. The World Health Organization’s Global Polio Eradication Initiative has estimated that there were 50 million worldwide paralytic polio survivors in the 20th century alone3.

The workings of polio as a disease were not known for many years. Slowly, scientists began to learn that the virus enters through the mouth and travels to the intestines where it begins to multiply for anywhere from 4-35 days. “The initial symptoms include fever, fatigue, headaches, vomiting, constipation (or less commonly diarrhea), stiffness in the neck, and pain in the limbs.”4 From the intestines, the virus moves to the bloodstream and eventually invades the central nervous system through nerve fibers. It begins to destroy the motor neurons, thus immobilizing muscles and causing the characteristic paralysis of severe cases. Usually the paralysis only affects the legs, but for some it causes quadriplegia and even death by asphyxiation when the paralysis affects the portions of the brain that control breathing. Researchers today know that only 1 in 200 cases is paralytic and 5-10% of paralytic cases result in death. However, there is still no cure for the disease; it can only be prevented5. Those who do contract it can be given physical therapy, but little else can be done for them.6

When the disease was first recognized, the medical community had no idea how to handle it. Of those who contracted the disease, not all got severe cases of it. A few had temporary paralysis but for most who experienced any kind of paralysis, it was permanent. The iron lung (an artificial means of respiratory support) and leg and arm braces became symbols of the disease’s more severe effects and the valiant efforts to aid in the suffering. Doctors were unsure of how to treat it and tried any number of things. One famous woman, Sister Elizabeth Kenny, began a clinic and treated patients by placing heat packs on their atrophied muscles and slowly working patients up to increased levels of mobility, attempting to wean them from the use of the iron lung. Many treatments were painful, and the suffering of those children stirred the hearts of researches and housewives alike. In the United States, the National Foundation for Infantile Paralysis, otherwise known as the March of Dimes, began a massive campaign to raise funds not only for sufferers and their families (who lived before the time of medical insurance), but more importantly to find a cure.

Early vaccination attempts in the 1930s were disastrous – either the vaccines were too weak to sustain immunity or they were so strong that they induced full-blown polio. At first, researchers did not know that there were three different (but closely related) viruses that caused the disease, and several vaccines came out that protected against one but not all of those viruses. Two researches in the early 1950s emerged with competing ideas of which kind of vaccine would work. Jonas Salk insisted that a killed vaccine, which used killed samples of the three major types of the poliovirus, was safe and effective. Alfred Sabin insisted that a live attenuated vaccine (which means that the virus injected is alive but a weakened form of the poliovirus) was the only one that could induce lasting immunity.

The March of Dimes funded them both, and it became a sort of race to see who would succeed first. Jonas Salk took an early lead and perfected his vaccine in 1952. He first tried it out on residents of a rehabilitation hospital for polio victims in order to see if the vaccine did, indeed, increase the antibodies in the blood against all three types of poliovirus. This seemed a safe testing ground since all of the patients had been exposed to the virus, but not all had been exposed to all three strains, thus the results offered him some idea of the vaccine’s effectiveness. When that was successful, he vaccinated his entire laboratory, himself, and his family and began testing the vaccine on other uninfected children. Finally, he decided to try a large-scale trial of the vaccine in 1954. Dr. Thomas Francis, an epidemiologist at the University of Michigan agreed to supervise the national field trial. He insisted that it be conducted as a double-blind, placebo-controlled trial. Half of the children received the vaccine and half did not, and neither the doctors, the patients, nor Salk himself knew which child got which. All of the records and later surveillance information about each child was shipped to him at the Vaccine Evaluation Center he created in Ann Arbor, Michigan. The results of this, the largest field trial in the history of the United States in which 1.8 million children participated, were released in spring of 1955: the group of children who got the vaccine were significantly less likely to contract polio than were the group of children who did not get the vaccine. In addition, the incidence of diseases not related to polio were the same between the two groups of children. As a result, the vaccine was licensed in time for the summer of 1955.7 Immediately, the number of polio cases in the United States plummeted (see graph in “Vaccines are Incredibly Effective at Preventing Disease”).

Not long afterward, Alfred Sabin refined his live attenuated formula, but he could not test the vaccine in the United States since so many had already been immunized using Salk’s vaccine, so he went instead to Russia to find new case subjects. Since vaccination had not begun there, polio was still raging. There (and in Singapore, Eastern Europe and Mexico), he vaccinated 4,500,000 people. There were very few side effects, and the vaccine was highly effective. After a few more tests, the United States licensed the vaccine for use in 1961, and it quickly replaced the Salk formula until 1999. Soon after licensure in the United States, the Sabin formula was proven to have caused extremely rare cases of paralytic polio8. Since at that point, the threat of wild poliovirus was much greater than the threat of Vaccine Associated Paralytic Polio (VAPP), authorities continued to administrate it. By 1999, the United States had been free of wild polio for many years and the problem of VAPP was deemed to be more problematic than continuing with the Sabin formula. Since the Salk formula has no history of VAPP, it is considered safer for the general public and almost as effective9, so that is what we use today in the United States.

Eventually, most countries switched over to the Sabin formula, and it is still the vaccine of choice for the World Health Organization’s Global Polio Eradication Initiative for several reasons. Not only does this vaccine, now called the Oral Polio Vaccine (OPV), provide antibody immunity from all three strains of poliovirus, but it also creates a local immunity in the intestines, the most important site for the multiplication of the virus in its early stages. Another advantage is its oral distribution which reduces the need for trained health professionals to administer it. It is very inexpensive, with each dose costing around $0.08 (US). Lastly, the OPV-vaccinated person sheds the attenuated virus through his stool, and in areas of poorer hygiene, this means that others around him will be immunized as well. The person vaccinated with the killed virus vaccine (IPV) can still be infected with polio and have it multiply in his gut since IPV does not provide that local immunity. This has become a concern of the eradication program, since circulating vaccine-derived poliovirus can still cause polio in areas where polio is no longer endemic (meaning no longer indigenous to the area). For this reason, the WHO has recommended that countries use OPV for outbreaks especially and that routine vaccination continues to be practiced until global eradication of the virus is confirmed10. The history of polio in this country and abroad is very different from those of many other diseases.

Because sanitation reduces a population’s immunity to the disease, it first began in the very places that were equipped to fight it – developing countries with the scientific and financial means to research and develop a vaccine. Yet politics and science had to work hand-in-hand to overcome the disease, and since the two have often clashed, it was not an easy battle. Now, a little over a century after the first epidemics cropped up, the world is very nearly polio free, thanks to mass vaccination. Perhaps this disease will someday be as powerless to harm as it was for so many centuries before it was recognized.


1. Aaron E. Klein Trial by Fury: the Polio Vaccine Controversy Scribner (New York, NY) 1972, p. xiv (picture)
2. Center for Disease Control (CDC) “Polio Vaccines” (Available online)
3. Global Polio Eradication Initiative (GPEI) “News and Documents: Fact sheet and FAQ” ( Available online )
4. Global Polio Eradication Initiative (GPEI) “Background: The Disease and Virus” ( Available online )
5. GPEI, News
6. GPEI, Disease
7. Aaron E. Klein, pp. 79-80
8. Ibid., pp. 149-151
9. CDC, p. 4
10. Global Polio Eradication Initiative “Post Eradication Recommendations” ( Available online )

Erica A. Sommerville is not a medical doctor but a college student. She does not dispense medical advice. Her aim is to educate the public about scientific issues. Please consult a board-certified medical doctor before making any medical decisions for yourself or your family.