Right, the swine flu pandemic of 2009 was basically a descendant of Spanish Flu. It continues to circulate, particularly in the last couple years - a majority of flu cases this last couple months have been the H1N1 strain that descends from Spanish Flu. We don't hear about it because newer and more deadly pathogens like COVID-19 have cropped up since.

I think most people in this thread are talking about 1918-1919, though, since that time period's a little more relevant for predicting what COVID-19 will do.