Poliomyelitis, commonly called polio, was first described in 1789, but not fully recognized until 1840. In the United States, it first became a feared disease when a small epidemic in 1894 struck Vermont, because it singled out children and often caused paralysis or death. A larger outbreak began in 1916, also striking the East Coast. Franklin D. Roosevelt, later president of the United States, was paralyzed from the waist down by the disease in 1921. Another large outbreak hit the West Coast in 1934. In the late 1940s and early 1950s, a major epidemic of the disease struck the entire United States, infecting tens of thousands each year.

As early as 1908, the cause of polio had been identified –– a virus. Jonas Salk, a medical doctor, had worked on the vaccine for the influenza virus during the 1940s. As the head of the Virus Research Laboratory at the University of Pittsburgh School of Medicine, he began the study of the virus causing polio. He confirmed the existence of three types of polio viruses and started growing them in cultures of monkey kidney tissue. He prepared vaccines by killing these viruses with formaldehyde. The killed viruses did not cause the disease, but did stimulate the production of antibodies that protect the human organism against the disease.

In 1952 Salk tested the vaccine on children who had already experienced polio and thus were immune to the virus. The vaccine increased the amount of antibodies in these children, elevating their immunity. The first trial on children who never had polio took place in 1954; it showed the vaccine to be safe and effective. Throughout the 1950s the incidence of polio was reduced drastically worldwide as a result of the Salk vaccine. By 1957 the number of new cases of the disease in the United States had been reduced from 35,000 in 1953 to 5600.

Albert Sabin, a medical doctor who also had studied the polio virus, prepared a different vaccine containing a live strain of a virus. This virus also stimulates the production of antibodies but is too weak to cause the disease itself. The Sabin vaccine, which (unlike the Salk vaccine) can be administered orally, was tested in large-scale trials in 1957 in the United States and other countries.

It was adopted in the Soviet Union and Europe in 1959, and was approved in the United States in 1961. It has two advantages over the Salk vaccine –– it can be administered orally and, since it is alive and therefore infectious, it provides some immunity to persons who come in contact with the one who takes the vaccine.

By 1964, two years after introduction of the Sabin vaccine, the number of new cases in the United States was reduced to 121 and by 1979 there were no new cases at all that originated in the United States. Around the world, however, the majority of people were still unvaccinated, so as many as 350,000 cases a year were still occurring in the late 1980s. In 1988 the World Health Organization (WHO) initiated a drive to eradicate polio completely, as another virus-borne disease, smallpox, had been defeated by vaccination.

By 2003 the disease had been eliminated (except for isolated cases) everywhere except India, Pakistan, and Nigeria, with fewer than 300 new cases in those nations.