context: The first polio vaccine was the inactivated polio vaccine.[1] It was developed by Jonas Salk and came into use in 1955.[1][6] The oral polio vaccine was developed by Albert Sabin and came into commercial use in 1961.[1][7] They are on the World Health Organization's List of Essential Medicines, the most effective and safe medicines needed in a health system.[8] The wholesale cost in the developing world is about US$0.25 per dose for the oral form as of 2014.[9] In the United States, it costs between $25 and $50 for the inactivated form.[10]
question: When was the polio vaccine developed?
answers.text: 1955 1955 1955