The first mass polio shots are given

On 23 February 1954, children at Arsenal Elementary School in Pittsburgh lined up for an injection against one of the era’s most feared diseases — the first shots of Jonas Salk’s polio vaccine, developed at the University of Pittsburgh.

Polio struck without warning, mostly children, sometimes leaving paralysis or a lifetime in an iron lung. Outbreaks emptied swimming pools and closed theaters each summer. Salk’s killed-virus vaccine offered the first real hope of stopping it.

The Pittsburgh shots were the prelude to a national field trial that would enroll close to two million children.

Led by Thomas Francis, that trial was among the largest medical experiments ever run. When results were announced in 1955, the vaccine was declared safe and effective, and mass immunization followed. U.S. polio cases soon fell from tens of thousands a year toward near-zero.