This is a similar infection to 'normal' so called 'Seasonal Flu' but it is caused by a different type of flu virus - the H1N1 subtype (it is sometimes called this too). This virus lived in pigs (whose old-fashioned name is swine) for a long time and didn't cause an illness in humans. In early 2009 it began to infect humans and caused a worldwide outbreak of the disease (also called a pandemic). Because our immune systems had never been exposed to this type of flu virus before it sometimes caused a much more serious infection than normal 'Seasonal Flu'. The media got very excited about the whole thing but the outbreak was not as bad as people thought it might be. Most people who caught it only had an illness similar to normal flu.