title: Influenza vaccine
context: Vaccination against influenza began in the 1930s with large scale availability in the United States beginning in 1945.[12][13] It is on the World Health Organization's List of Essential Medicines, the most effective and safe medicines needed in a health system.[14] The wholesale price in the developing world is about $5.25 USD per dose as of 2014.[15] In the United States, it costs less than $25 USD as of 2015.[16]
question: When was the flu vaccine introduced?
answers: began in the 1930s