It's hard for anyone under 60 to remember the panic that polio caused before the 1960s. It was a crippling disease, often leaving victims hunched over for life. It was also contagious, adding to the fear factor.
Dr. Jonas Salk developed the first polio vaccine in the 1950s, and families lined up to get their shots. The government and other organizations flooded the mail with immunization cards like this one, with spaces for each family member.
Later, the shots were given in school. The typical shot was a pressure activated needle with several smaller needles around it in a circular shape. The shot was usually given in the upper arm, and the circular pattern sometimes left a scar with a circle of dots and a larger dot inside.
Obviously even the ancient Spartans knew this, as evidenced by this still from "300". Click to enlarge.