Before COVID-19, the Spanish flu was the most deadly pandemic in the world during the 20th century. Also known as the flu pandemic of 1918 was one major influence pandemic that lasted for at least two years. After the outbreak of the coronavirus pandemic, people have been referring to the Spanish flu outbreak in an attempt to gauge how the COVID-19 might last. The Spanish flu had arisen in three waves. But these waves were not simultaneous all over the world. The origin of the Spanish flu virus still remains uncertain. The earliest incidents were recorded among US military personnel in Kansas.