2009 H1N1 (referred to as “swine flu” early on) is a new influenza (flu) virus causing illness in people. This new virus was first detected in people in the United States in April 2009. This virus is spreading from person-to-person worldwide, in much the same way that regular seasonal flu viruses spread. On June 11, 2009, the World Health Organization (WHO) signaled that a pandemic of 2009 H1N1 flu was underway. On June 16, 2009 the first cases of H1N1 flu were confirmed for Merced County. Most people infected with this 2009 H1N1 flu virus in the United States have had mild disease, but some have had more severe illness.