"Polio Vaccine Evaluation Results" Primary Source eText

Primary Source

Jonas Salk, inventor of polio vaccine, administers an injection of vaccine to David Rosenbloom. AP/WIDE WORLD PHOTOS. Jonas Salk, inventor of polio vaccine, administers an injection of vaccine to David Rosenbloom. AP/WIDE WORLD PHOTOS. Published by Gale Cengage AP/WIDE WORLD PHOTOS.

Press release

By: Thomas Francis

Date: April 12, 1955

Source: Francis, Thomas. "Polio Vaccine Evaluation Results." Press Release. University of Michigan, April 12, 1955. Available online at ; website home page: http://www.med.umich.edu/medschool/chm/index.htm (accessed June 9, 2002)

About the Author: Thomas Francis (1900–1969), the lead researcher on the project described in this press release, was born in Gas City, Indiana, in 1900 and received his M.D. from Yale University in 1925. He isolated two strains of influenza between 1934 and 1940 and developed vaccines against both. In 1954 the University of Michigan appointed him to the National Foundation for Infantile Paralysis, where he tested Jonas Salk's polio vaccine.


The development of vaccines is one of medicine's triumphs. Edward Jenner, an eighteenth-century British physician, inaugurated the era of vaccination, concentrating on smallpox. He noted that smallpox survivors, including those infected with a mild case, were immune to the disease. Yet to deliberately infect a person with smallpox to confer immunity was dangerous, for the infection could kill the person. So he turned his attention to cowpox, a mild disease contracted from cattle, noting that a person infected with it also became immune to smallpox. He reasoned that if he infected a person with cowpox, he could make that person immune to smallpox. In 1796 he tested this hypothesis by infecting a young boy with cowpox, then, when the boy recovered, injecting him with smallpox. The boy developed no symptoms of the disease. Jenner had developed the first vaccine.

Jenner had no idea, however, why cowpox conferred immunity to smallpox. Modern medicine would discover that a dead or attenuated strain of a virus or bacterium or that of a closely related virus or bacterium causes the body to produce antibodies. Once the body has manufactured these antibodies, it will quickly produce them in large numbers if a person contracts a virulent strain of the bacterium or virus, killing it and thereby preventing it from spreading throughout the body.


Less lethal than smallpox, polio nonetheless infected some 20,000 Americans a year in the early 1950s. Fortunately vaccination works against polio as it does against smallpox. The American physician Jonas Salk began to study polio when he became head of the Virus Research Laboratory in 1947 at the University of Pittsburgh. He isolated three polio strains, demonstrating that dead cultures conferred polio immunity in monkeys. In 1952 he began testing the cultures on children who had recovered from polio and then on children who had never had the disease. In all cases the inoculations conferred immunity to polio. In recognition of his work, President Jimmy Carter awarded Salk the Presidential Medal of Freedom in 1977.

In 1954 Thomas Francis Jr. launched a mass field trial of the vaccine, reporting in April 1955 that the vaccine was a success and that it held the potential to eradicate the disease. He proved to be correct, for between 1961 and 1981 only six Americans contracted polio. Like the smallpox vaccine, the polio vaccine tamed a scourge of humanity.

Primary Source: "Polio Vaccine Evaluation Results"

SYNOPSIS: In this press release Thomas Francis Jr. announces that "the [polio] vaccine works. It is safe, effective, and potent." He also announces that medicine now has the means of protecting children from polio, implying that the vaccine could eradicate the disease.

Ann Arbor: The vaccine works. It is safe, effective, and potent.

Dr. Thomas Francis, Jr., U-M Director of the Poliomyelitis Vaccine Evaluation Center, told an anxious world of parents that the Salk vaccine has been proven to be up to 80-90 percent effective in preventing paralytic polio.

At a meeting of over 500 scientists and physicians and before the penetrating eyes of cameras and powerful spotlights, Dr. Francis spoke on the effectiveness of the Salk vaccine. The meeting was held at the Rackham Auditorium in Ann Arbor under the joint sponsorship of the National Foundation for Infantile Paralysis and the University of Michigan.

Dr. Francis declared the vaccine had produced "an extremely successful effect" among bulbar-patients in the areas where vaccine and an inert substance had been tried interchangeably.

Financed by nearly one million dollars worth of dimes which have been donated to the National Foundation, the Francis Report may slow down what has become a double-time march of disease to a snail's pace.

In strong statistical language the historic trial of a vaccine and its subsequent analysis was revealed. Over 113 pages in length, the Report at long last called a halt to speculations and finally reinforced laboratory findings with concrete field evidence. There can be no doubt now that children can be inoculated successfully against polio.

There can be no doubt that humanity can pull itself up from its own bootstraps and protect its children from the insidious invasion of ultramicroscopic disease.

For one thing, what was feared turned out to be unfounded—the vaccine proved incredibly safe. Reactions were nearly negligible. Only 0.4 percent of the vaccinated children suffered minor reactions.

An even smaller percent (0.004-0.006) suffered so-called "major reactions."

And the persistence of protection appears reasonably good. When good antibody responses were obtained from vaccination, the report said "the effect was maintained with but moderate decline after five months."

Distribution of antibody levels among vaccinated persons was much higher than that in the control population from the same areas.

Out of a total population of 1,829,916 children a total of 1013 cases of polio developed during the study period and were reported to the Center.

In placebo control areas, where vaccine was interchanged with an inert substance, 428 out of 749,236 children contracted the disease.

In the observed control areas where only second graders were inoculated, 585 cases out of 1,080,680 children developed the disease.

Percentages in the placebo areas were: 67.5 paralytic, 17.6 non-paralytic, 7.2 doubtful, and 7.6 not polio.

Specifically, 33 inoculated children receiving the complete vaccination series became paralyzed in the placebo areas. This is opposed to 115 uninoculated children. Similarly, in the observed areas there were 38 such children who became paralyzed, as opposed to 330 uninoculated children.

There were four deaths among children who received placebo; none among the vaccinated. In observed areas there were 11 fatalities; none among children receiving the vaccine.

Only one child who had been inoculated with the vaccine died of polio, and this death followed a tonsillectomy two days after the second injection of the vaccine in an area where polio was already prevalent.

The Report also stated that in no area did Type II virus prevail. There was, however, prevalence in certain areas of Types I and III.

Marked sociological differences were noted by the U-M's Survey Research Center among the participating and non-participating children in the study. For example, there was a higher proportion of children participating who had been vaccinated against small-pox, diphtheria, and whooping cough than among the non-participants. Significant auxiliary findings were:
  1. The vaccine's effectiveness was more clearly seen when measured against the more severe cases of the disease;
  2. Although data were limited, findings in Canada and Finland support the Report in showing a significant effect of the vaccine among cases from whom virus was isolated;
  3. Vaccination protected against family exposure. Only 1 out of 233 inoculated children developed the disease, while 8 out of 244 children receiving placebo contracted the disease from family contact. In picking the field trial areas, the National Foundation scored a major victory. Although in placebo areas cases were 27 per cent under the 1949-53 average, and 12 per cent less in the observed control areas, it was found that there had been a 26 per cent greater increase per 100,000 in trial areas as in non-trial areas.

This meant that trial areas were appropriately selected for the best testing conditions for the vaccine. The field trials and the evaluation were made possible by grants totalling $17,500,000 in March of Dimes Funds from the National Foundation for Infantile Paralysis.

Further Resources


Carter, Richard. Breakthrough: The Saga of Jonas Salk. New York: Trident, 1965.

Cryz, Stanley J. Immunotherapy and Vaccines. New York: VCH, 1991.

Kaufman, Stefan H. E. Concepts in Vaccine Development. New York: Walter & Gruyter, 1996.

Plotkin, Stanley A, and Edward A. Mortimer, eds. Vaccines. Philadelphia: W. B. Saunders, 1988.

Rowland, John. The Polio Man: The Story of Dr. Jonas Salk. New York: Roy Publishers, 1960.

Salk Vaccine. Hearings Before the Committee on Banking and Currency, House of Representatives, Eighty-Fourth Congress. Washington: GPO, 1955.


Grady, Denise. "As Polio Fades, Dr. Salk's Vaccine Re-emerges." The New York Times, December 14, 1999, D1.

Johnson, Amy. "Jonas Salk." Ideals, July 2001, 24–26.

Marks, Marilyn. "Jonas Salk." Science Teacher, February 2002, 81–83.


Marching to a Different Drummer: The Life and Career of Jonas Salk. Burlington, N.C.: Carolina Biological Supply Company, 1991, VHS.

Viruses: What They Are and How They Work. Chicago: Encyclopedia Britannica Educational Corporation, 1988, VHS. War Against Polio. London, England: BBC, 1977, VHS.