Jonas Salk had an idea to eliminate all strains of polio at once: Grow the polio viruses, kill them, then inject healthy children with the dead viruses. The dead viruses unable to reproduce, would not harm the children, but their immune systems would detect the invading viruses and producing antibodies repel any live polio virus in the future. His trials were successful.
Bernice Eddy at NIH was told to safety-test the polio vaccine. After she injected the vaccine in monkeys, they fell paralyzed. Eddy realized that the virus in the vaccine was alive and ready to multiply. She sent pictures of the paralyzed monkeys to NIH's management to warn them but the mass inoculation proceeded on schedule. Within days, children fell sick from polio, some were crippled, some died.