Some facts about the influenza pandemics of the 20th century:
Spanish flu - Caused by an earlier H1N1 virus. Started in the spring of 1918, subsided by 1920. Estimated to have killed 30,000 to 50,000 Canadians and at least 50 million people worldwide, though poor data from some developing countries means the actual death toll may have been substantially higher. Healthy young adults hardest hit. Overall death rate among cases between 2.0-2.5 per cent.
Asian flu - Caused by an H2N2 virus. Started in 1957, spread in two waves into 1958. Estimated to have killed upwards of one million.
Hong Kong flu - Caused by an H3N2 virus. Hit in 1968-69. Estimated to have killed about one million people.