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Timeline representing four human influenza pandemics between 1918 and March 2020. The first influenza pandemic known as “Spanish flu” originated in chicken in 1918. The second flu pandemic (Asian flu) and the third flu pandemic (Hong Kong flu) originated in chicken in 1957 and 1968, respectively. The most recent influenza pandemic known as “Swine flu” originated in swine in Mexico during March–May 2009.
