The 1918 Spanish flu was a severe influenza pandemic that occurred between 1918 and 1919. It is estimated to have infected one-third of the world's population and resulted in the deaths of approximately 50 million people globally. The virus spread rapidly due to the movement of troops during World War I and the crowded conditions in cities. Unlike typical flu strains, the Spanish flu disproportionately affected young, healthy adults. Symptoms included high fever, severe respiratory issues, and pneumonia. Public health measures, such as quarantines and mask-wearing, were implemented in many areas to control the outbreak, but the virus still had a devastating impact worldwide.