When did the polio vaccine becomes available?
['Inactivated poliovirus vaccine (IPV), developed in the USA by Jonas Salk in the early 1950s, was field tested in 1954,', 'the use of an oral polio vaccine (OPV) during a vaccination campaign launched by the Wistar Institute, Philadelphia, PA, USA, in the Belgian Congo in 1958 and 1959. ']
['Inactivated poliovirus vaccine (IPV), developed in the USA by Jonas Salk in the early 1950s, was field tested in 1954,', 'The Salk polio Vaccine was field tested in 1954.']
['1954']