"Safe, effective, and potent."
With these words on April 12, 1955, Dr. Thomas Francis Jr., director of the Poliomyelitis Vaccine Evaluation Center at the University of Michigan School of Public Health, announced to the world that the Salk polio vaccine was up to 90% effective in preventing paralytic polio.
Dr. Francis made the announcement to a crowd of scientists and reporters at the University of Michigan's Rackham Auditorium, concluding his two-year national field trials of the poliomyelitis vaccine developed by his former student, Jonas Salk. Francis was chair of the School of Public Health Department of Epidemiology where Salk did postgraduate training.
Over 1,800,000 children participated in the field trials, which were unprecedented in magnitude.