http://www-micro.msb.le.ac.uk/Tutorials/polio/polio10.html

A vaccine

Jonas Salk (1914-1995) believed that the same inactivated virus techniques which had yielded the influenza vaccine would yield a safe and effective poliovirus vaccine. In the spring of 1952, after two years of development, Salk began experimental trials of his his killed vaccine. Large scale trials were begun in 1954. The initial vaccine was 60-70% effective against type I paralysis, over 90% effective against type II and type III, and 94% effective against bulbar poliomyelitis, the type that affects breathing (the efficiency was improved even further with later developments). The vaccine was immediately put into widespread use.

Then, disaster struck. The polio vaccine manufactured by Cutter Laboratories in Berkeley, California, had been improperly inactivated and contained live poliovirus. Two hundred four people contracted polio from the bad vaccine, over one hundred fifty were paralyzed, and eleven died. The Cutter vaccine was recalled, but the vaccinations with other batches continued. The vaccine was in short supply. By 1957, when it was widely available, though, no one seemed interested...