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Influenza A virus is a subtype of influenza A virus and was the most common cause of human influenza in 2009. More at
Wikipedia
Pandemic H1N1/09 virus - The Pandemic H1N1/09 virus is a swine origin Influenza A virus subtype H1N1 virus strain responsible for the 2009 flu pandemic.
2009 flu pandemic - The 2009 flu pandemic was a global outbreak of a new strain of H1N1 influenza virus, often referred to as "swine flu".
1918 flu pandemic - The 1918 flu pandemic was an influenza pandemic that spread widely across the world.
