MBB & WBB: New Covid Cancellations and Fan Restrictions History: "What’s even more remarkable about the 1918 flu, say infectious disease experts, is that it never really went away. After infecting an estimated 500 million people worldwide in 1918 and 1919 (a third of the global population), the H1N1 strain that caused the Spanish flu receded into the background and stuck around as the regular seasonal flu.
"But every so often, direct descendants of the 1918 flu combined with bird flu or swine flu to create powerful new pandemic strains, which is exactly what happened in 1957, 1968 and 2009. Those later flu outbreaks, all created in part by the 1918 virus, claimed millions of additional lives, earning the 1918 flu the odious title of “the mother of all pandemics.” ...
"...Since the whole world had been exposed to the virus, and had therefore developed natural immunity against it, the 1918 strain began to mutate and evolve in a process called “antigenic drift.” Slightly altered versions of the 1918 flu reemerged in the winters of 1919-1920 and 1920-1921, but they were far less deadly and nearly indistinguishable from the seasonal flu.
“The 1918 flu definitely lost its real virulence by the early 1920s,” says Taubenberger."
https://www.history.com/news/1918-flu-pandemic-never-ended