Influenza is a respiratory infection caused by the influenza virus. Various strains of the virus circulate throughout the world year-round, causing local outbreaks. In Canada, flu season usually runs from November to April and an estimated 10-25% of Canadians may get the flu each year. Although most of these people recover completely, an estimated 4,000 to 8,000 Canadians, mostly seniors, die every year from pneumonia related to flu and many others may die from other serious complications of flu.