CASE STUDY The 2009 swine flu pandemic was an influenza pandemic that lasted for about 19 months, from January 2009 to August 2010, and was the second of two pandemics involving H1N1 influenza virus (the first being the 1918–1920 Spanish flu pandemic). First described in April 2009, the virus appeared to be a new strain of H1N1 which resulted from a previous triple assortment of bird, swine, and human flu viruses that further combined with a Eurasian pig flu virus,[12] leading to the term "swine flu". Some studies estimated that the actual number of cases including asymptomatic and mild cases could be 700 million to 1.4 billion people—or 11 to 21 percent of the global population of 6.8 billion at the time.[9] The lower value of 700 million is more than the 500 million people estimated to have been infected by the Spanish flu pandemic.[14] However, the Spanish flu infected a much higher proportion of the world population at the time, with the Spanish flu infecting an estimated 500 million people, which was roughly equivalent to a third of the world population at the time of the pandemic.
