Poliomyelitis and the Salk Vaccine: Introduction

On April 12, 1955, the world anxiously awaited the announcement of the results of the largest vaccine field trial in history. The announcement would report on the effectiveness of the polio vaccine developed by Dr. Jonas Salk of the University of Pittsburgh. In 1954, over 1.8 million elementary school children took part in a field trial to test the Salk vaccine. The results of the field trials were rigorously evaluated at the University of Michigan Polio Evaluation Center by Dr. Thomas Francis of the School of Public Health. From the stage of the Rackham Auditorium Francis faced a gathering of distinguished scientists and an anxious crowd of reporters as he read his report.

The Francis report was the culmination of a year-long field trial of the Salk vaccine, unprecedented in its scope and magnitude. Using a double-blind method of statistical analysis, where neither patient nor administering physician knew if the inoculation was the Salk vaccine or a placebo, 444,000 children were given the vaccine and 210,0000 the control substance. In all, approximately 1,800,000 children in 217 areas of the United States, Canada, and Finland were involved in the field trial.

T. Frarcis and B. O'Conner

Thomas Francis and Basil O'Connor
(Thomas Francis Papers, box 65)

As a statistical exercise, the polio field trial was unique in the annals of epidemiological study. Francis and his staff at the University of Michigan produced some 1,800,000 IBM punch cards containing 144,000,000 pieces of information about the test children. On staff at the Polio Evaluation center was a small army of statisticians, epidemiologists, and clerical and support personnel. More than 10 individuals were involved in tabulating the data received from public health officials and doctors participating in the field trials. According to a university press release, more than 300,000 individuals participated in the field trials: 20,000 physicians and public health officers, 40,000 registered nurses, 14,000 school principals, 50,000 teachers, and 200,000 volunteer workers.

photo of tabulating machine

Tabulating results of polio vaccine field tests
(University of Michigan News and Information
Service, Box E-13 (print), A-9 (neg.))

Dr. Francis jealously guarded the findings of the test up until the last moment. Premature disclosure, especially if misreported, could adversely affect the continuing struggle to find a cure for polio. Even Dr. Salk did not know the details of the test results, though he certainly must have had some idea that the vaccine was effective. Swarms of press and TV and radio reporters crowded outside of the Rackham auditorium hoping to grab a copy of the printed report as it arrived. One press report described the scene: "The releases were in boxes on a hand truck. To avoid a crush, public relations men from the university began throwing the releases into the crowd. But still hands grabbed at the boxes. In the next few seconds pandemonium prevailed. Then there was a dash for the couple of dozen typewriters in the press room and for a battery of telephones."1

distributing polio press release

Distributing the Salk vaccine press release and
summary field trials report, Rackham Auditorium,
April 12,1955 (Michigan Bell Telephone Company
Photographs, Box 18.)

"Safe, effective, and potent" were the words that Dr. Francis spoke, announcing to the world that the Salk polio vaccine was 60-90% effective in preventing paralytic polio. The long campaign against this virulent childhood disease, though certainly not over, was about to enter the final stages. Within a generation the scourge of polio would be but a memory to most Americans.

The date selected for the announcement, April 12, 1955, was the tenth anniversary of the death of Franklin D. Roosevelt, perhaps the most famous polio victim, and founder of the National Foundation for Infantile Paralysis, better known as the March of Dimes. Francis was joined on stage by Jonas Salk and Basil O'Connor, president of the National Foundation for Infantile Paralysis. Other polio experts also spoke, but without question the day belonged to Salk and Francis.

Vaccine Summary report

The report the press and the world was waiting for.

The results announced by Francis effectively marked the beginning of the end of polio as the most life-threatening and debilitating public health threat to the children of the United States. Jonas Salk knew full well the value of what Francis had accomplished. Pausing in his presentation to the press, he paid tribute to his former teacher. "For Dr. Francis, whatever is worth doing is worth doing well. He could not do otherwise. His kind of objectivity is rare, even among scientists--and it is the kind that in human terms is called honesty. He is his own severest critic--for which he has both the respect and admiration of his colleagues and students who strive to attain such stature as you have observed during this past year."2


  1. Newspaper article by Dick Shearin "Bedlam Prevails in Press Room Before Salk Polio Report Release" Dayton Daily News, April 13, 1955 (clipping in U-M News and Information Services, Box 25.
  2. "Introductory Remarks by Jonas E. Salk, April 12, 1955" (U-M News and Information Services, Box 9)