How did the 1918 flu end?

By the summer of 1919, the flu pandemic came to an end, as those that were infected either die d or developed immunity. Almost 90 years later, in 2008, researchers announced they'd discovered what made the 1918 flu so dea d ly: A group of three genes enabled the virus to weaken a victim's bronchial tubes and lungs and clear the way for bacterial pneumonia. Since 1918, there have been several other influenza pandemics, although none as de adly. A flu pandemic from 1957 to 1958 k illed around 2 million people worldwide, including some 70,000 people in the United States, and a pandemic from 1968 to 1969 kill ed approximately 1 million people, including some 34,000 Americans. More than 12,000 Americans perished during the H1N1 (or "swine flu") pandemic that occurred from 2009 to 2010.