Even isolated Alaskan towns got decimated by Spanish flu. These things find their way around.
Found this when looking, which describes how some areas were able to delay transmission and had vastly reduced fatality rates because of it (hopefully Tim will take note).
https://www.bbc.com/future/article/20181023-the-places-that-escaped-the-spanish-flu
Moral of their story: “These communities basically shut themselves down,” explains Howard Markel, an epidemiological historian at the University of Michigan who was one of the authors of the study. “No one came in and no one came out. Schools were closed and there were no public gatherings. We came up with the term ‘protective sequestration’.