Table of Contents • I. Poliomyelitis, Treatment, and Prevention Prior to 1955 • A. Poliovirus and Poliomyelitis • B. The Endemic Phase (Antiquity to ~1880) • C. Epidemic Emergence (1880-1920) • D. The Epidemic Phase (1920-1955) • E. The Path to a Vaccine • II. The Arrival of the Salk Polio Vaccine: Documents, April-July 1955 • III. Postscript - Polio Prevention after Jonas Salk • IV. Bibliography and Resources • V. Student Assignments • VI. Catalogue of Sources

Section I: Poliomyelitis, Treatment, and Prevention Prior to 1955

A. Poliovirus and Poliomyelitis

Polio, short for poliomyelitis, is a viral disease transmitted from human to human that can cause paralysis throughout the body. "Poliomyelitis" is derived from Greek roots referring to inflammation of the spinal cord, a symptom of severe cases that can lead to paralysis. At its height, the disease received major attention because it was the only common illness that could cause a previously healthy child or infant to be suddenly and rapidly paralyzed or even killed.

Polio is caused by a virus (poliovirus) and is transmitted through the fecal-oral route, meaning that the virus is harbored in the digestive tract and present in saliva, vomit, and feces. About 95 percent of poliovirus infections cause no symptoms, and afterwards the person usually becomes immune to another polio infection.¹ Polio primarily affects children because young people are less likely to have prior exposure to the virus. The five percent of infections that do show symptoms have three stages: abortive poliomyelitis, non-paralytic poliomyelitis, and paralytic poliomyelitis. All three infections usually begin with a fever, and perhaps a sore throat or headache. Because of the similarity of these symptoms to more common, milder childhood illnesses such as the flu, it took doctors a very long time to identify polio, and early diagnosis is still difficult. Most cases of polio subside at the abortive phase. Parents may think their child has the flu, and he or she recovers in a few days without any lasting symptoms.

In a small number of cases (about three percent), the disease advances to the non-paralytic phase. These flu-like symptoms (headache, fever, general discomfort, and vomiting) match those of abortive polio, but are usually more severe. They patient may also experience minor stiffness in the legs, back, and neck. Many polio infections end here, and the patient recovers completely. In the most extreme cases (about one percent), paralytic polio occurs, and the victim loses control of affected muscles in a matter of days. Poliovirus causes paralysis by infecting the nerve cells responsible for movement, and patients lose control of muscles wherever the nerve cells controlling these muscles get affected, most commonly in the arms, legs or those in the chest that control breathing. In a more severe, but less common form, the virus infects the motor neurons of the brainstem, inhibiting the ability to breathe, speak, and swallow, potentially causing death. In some cases of paralytic polio the virus only damages the neurons and some recovery is possible; in others, the paralysis is permanent.²

Physicians can confirm suspicions of polio when they see signs of paralysis after a fever or when fluid taken from an inflamed spinal cord indicates the presence of the virus. There is no cure for polio, but vaccines have been available for over 50 years. Following the arrival of polio vaccines in the 1950s, the incidence of the disease in the United States declined from a high of 500,000 cases each year to fewer than 2,000 in 2007 - a reduction rate of 99.6 percent.³

Continue to The Endemic Phase (Antiquity to 1880s)

¹ American Academy of Pediatrics. "Poliovirus Infections" In Pickering, LK, ed. Red Book. Available at: http://aapredbook.aappublications.org.
² "Polio." MayoClinic. July 2008 http://www.mayoclinic.com/health/polio/DS00572.
³ Carter, Rachel B. "50th Anniversary of Salk Polio Vaccine." UNICEF. http://www.unicef.org/immunization/index_25987.html.