What year was the polio vaccine first widely distributed?

In the early 1950s, the first successful vaccine was created by US physician Jonas Salk. Salk tested his experimental killed-virus vaccine on himself and his family in 1953, and a year later on 1.6 million children in Canada, Finland, and the USA. The results were announced on 12 April 1955, and Salk’s inactivated polio vaccine (IPV) was licensed on the same day. By 1957, annual cases dropped from 58 000 to 5600; by 1961, only 161 cases remained.

Source: WHO