Pandemic H1N1 (originally referred to as swine flu) is a respiratory disease caused by type A H1N1 influenza virus. Human cases of pandemic H1N1 influenza started showing up in the U.S. in late March 2009, and quickly spread throughout the country and the world. In June 2009, the World Health Organization declared a pandemic of the new virus. Most people with pandemic H1N1 get better with bed rest, good nutrition, and use of over-the-counter medications to relieve symptoms. Regular flu vaccines do not generally protect against pandemic H1N1 flu. However, seasonal influenza is a serious illness that kills approximately 36,000 people in the U.S. each year. It is important to get vaccinated against the flu every year.