Animal research was crucial to identifying what caused polio and finding a vaccine. In 1908 Drs. Karl Landsteiner and Erwin Popper proved that polio was an infectious disease by showing that monkeys injected with tissue from a person who died of polio would become ill with the disease. We now know that polio is transmitted when bodily wastes from a person who has the disease contaminate food or water, which then is ingested by another person. Polio was difficult to stop because it is caused by a virus.
Viruses are also harder to isolate than bacteria.
In 1949 Drs. John Enders, Frederick Robbins, and Thomas Weller made a breakthrough when they figured out how to grow the polio virus in cell cultures. This achievement earned them a Nobel Prize. During the 1950s, Drs. Jonas Salk and Albert Sabin developed two different polio vaccines.