However, the Spanish Flu had some things going for it that were rather unique and unlikely to ever occur again: vast displacements of vast numbers of people, vast numbers of people in poor health due to years of deprivation as a result of food shortages and young adults being in especially poor health (Normally men of fighting age are the healthiest members of a population. After four years in the trenches, not so much).

The Spanish Flu clouds the issue somewhat, as it's always the first thing people think of when they hear the words "flu epidemic" but it's also the most unusual of all such epidemics.