A Brief History of Polio

From Ancient Egypt to the 20th Century

Polio has probably caused paralysis and death for most of human history. The oldest clearly identifiable reference to paralytic poliomyelitis is an Egyptian stele (stone engraving) over 3,000 years old. Cases of poliomyelitis tended to be rare in ancient times, though, as sanitation was generally poor. With improvements in waste disposal and the widespread use of indoor plumbing in the 20th century, epidemics of polio began to occur with regularity in the developed world, primarily in cities during the summer. Because sewage was dumped away from the drinking water supply (a development which helps combat a number of other diseases, including cholera), babies were much less likely to be infected with polio and gain protective immunity. As the children got older and began playing with others, swimming in public pools, and going to school, they were more likely to be exposed to the virus, which was then more likely to cause paralytic poliomyelitis.

H.L. Mencken writes of polio epidemics occurring virtually every summer in Baltimore during his childhood in the late 1890s, and this tragic cycle continued through the 1950s. Though the virus only paralyzes about 1% of the individuals it infects (most infections are asymptomatic or result only in a self-limiting diarrhea), it tends to be transmitted very easily under the right conditions. One percent of all children in a large city translates into thousands of cases, and the emotional and economic impact of such epidemics was staggering. The brochure below was distributed a few years before the vaccines were available.

Vaccination and Eradication

By the time of the Great Depression, paralytic poliomyelitis was perhaps the most feared disease known. Polio struck fast, there was no cure, and it crippled its victims for life. Hobbling on crutches, rolling in wheelchairs, or lying immobile in giant iron lungs, the legions of sufferers accumulated from year to year. Even the exact mechanism of polio's transmission was a hotly debated subject for many years, so many areas were placed under strict quarantine when cases of the disease began to manifest themselves. Only the fear surrounding AIDS can rival the feelings people had about polio in the first half of this century.

President Franklin Roosevelt declared a War on Polio during his administration, and the tremendous resources of postwar America were brought to bear on the problem of developing a vaccine. From the beginning of this effort, it was clear that such a vaccine was at least theoretically feasible, as contrasted with such pathogens as malaria and HIV, where no such assurance exists. In the early 1960s, the work bore fruit, first with the Salk vaccine, and soon after with the Sabin virus strains.

Salk used chemical and heat treatment to kill poliovirus, then injected this inactivated virus into patients. The proteins of the destroyed virus "taught" the patients' immune systems to recognize polio, and they were then protected from subsequent infection. Sabin's approach was to grow the virus in the laboratory under a variety of conditions, allowing it to accumulate mutations. Ultimately, this resulted in an attenuated virus which could be given to a patient orally. The weaker virus replicates normally in the intestine, but cannot grow well enough to invade the central nervous system. Once again, the immune system "learns" to recognize polio, and this confers protection.

Once the Sabin and Salk vaccines were proven effective, the disease was rapidly eradicated throughout most of the industrialized world. The economic effect has been enormous; it has been calculated that the polio vaccine pays for the costs of its development approximately every three weeks. The benefit to the United States alone for this single breakthrough runs into the trillions of dollars. The social impact has been incalculable. The crutches, wheelchairs, and iron lungs of polio victims have at last been banished from children's and parents' nightmares, at least in the developed world.

Recently, the World Health Organization embarked on a campaign for the worldwide eradication of polio. If this plan is completed successfully, it will conclude the second deliberate destruction of a virus by humans, and stand as the final victory in Roosevelt's other war.

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