Poliomyelitis, more commonly known as polio, is an infectious disease caused by an enterovirus of the same name. Fear of polio in the U.S. was second only to fear of nuclear war, in the post-war years, until Jonas Salk developed an effective vaccine. 
Polio, like most enteroviruses, is transmitted by the fecal-oral route, especially from ingestion of contaminated water.
Most cases (about 95%) of polio are asymptomatic, or cause minor respiratory or gastrointestinal symptoms. About 1 of every 1000 cases leads to paralytic polio.
Previously widespread in the US, polio is now all but eradicated here. Until vaccines were developed in the 1950s, parents spent their summers in fear that their children would be struck down. Two basic types of vaccine were developed:
- Oral Polio Vaccine (OPV). This vaccine makes use of a live-attenuated form of the virus. It is administered orally, infects the host, and is spread in the same way as polio. It does not cause paralytic polio. One advantage of this vaccine is that it can "passively" vaccinate those who do not get vaccinated normally. Unfortunately, immunocompromised people can become quite ill from exposure, so this vaccine is largely being replaced in the US.
- Inactivated polio vaccine (IPV). This is an injected vaccine that is now widely used in the US.
The eradication of polio in India has largely been a Western enterprise. 
Child being vaccinated in Afghanistan