Franklin Mint – History of the US – Polio Vaccine Declared Effective – 1955 – 45mm Proof Bronze Medal – Apr 1 – Senate ratifies treaty to end U.S. occupation of West Germany – Apr 12 – Report on Salk vaccine test reveals that it gives immunity against poliomyelitis – Sept 24 – The nation worried by President Eisenhower’s heart attack – Dec 5 – Merger of AFL and CIO unions.