 The 2009 flu pandemic or swine flu was an influenza pandemic , and the second of the two pandemics involving H1N1 influenza virus ( the first of them being the 1918 flu pandemic ) , albeit in a new version . First described in April 2009 , the virus appeared to be a new strain of H1N1 which resulted when a previous triple reassortment of bird , swine and human flu viruses further combined with a Eurasian pig flu virus , leading to the term " swine flu " . 
