The 2009 H1N1 influenza, commonly known as the "swine flu," is a novel strain of the influenza virus that emerged in the spring of 2009. It was initially identified in Mexico and quickly spread across the globe, leading the World Health Organization (WHO) to declare it a pandemic in June 2009. This strain is a reassortment of four different influenza viruses: North American swine influenza, North American avian influenza, human influenza, and swine influenza viruses typically found in Asia and Europe.
