On April 26, 1954, the Salk polio vaccine field trials, involving 1.8
million children, began at the Franklin Sherman Elementary School
in McLean, Virginia. Children in the United States, Canada and
Finland participated in the trials, which used for the first time the
now-standard double-blind method, whereby neither the patient
nor attending doctor knew if the inoculation was the vaccine or a placebo.

One year later, on April 12, 1955, researchers announced the vaccine
was safe and effective and it quickly became a standard part of childhood immunizations in America.