Brief History of Pandemics Fortunately for humans, pandemics are relatively rare. In fact, there were only three in the last one hundred years, and they varied in severity. The 1918 Spanish Flu was the most severe. It is estimated that approximately 20 to 40 percent of the worldwide population became ill and that over 50 million people died. Between September 1918 and April 1919, approximately 675,000 deaths from the flu occurred in the U.S. alone. One of the most unusual aspects of the Spanish flu was its ability to kill young adults. It was later determined that the 1918 pandemic was caused by an avian influenza. In February 1957, the Asian influenza pandemic was first identified in the Far East. The virus came to the U.S. quietly, with a series of small outbreaks over the summer of 1957. The elderly had the highest rates of death. Although the Asian flu pandemic was not as devastating as the Spanish flu, about 69,800 people in the U.S. died. In early 1968, the Hong Kong influenza pandemic was first detected in Hong Kong. The first cases in the U.S. were detected as early as September of that year, but illness did not become widespread in the U.S. until December. Those over the age of 65 were most likely to die. The number of deaths between September 1968 and March 1969 for this pandemic was 33,800, making it the mildest pandemic in the 20th century. For a more detailed description of the pandemics and pandemic threats in the last 100 years, go to pandemicflu.gov/general/historicaloverview.html.