/sci/ - Science & Math

How did the Spanish Flu pandemic end?

Most of what I found says something like "Infected/spreaders either died or became immune", but that sounds like BS with the 10% fatality rate.

Another theory was "less deadly strains emerged and had a selection bias due to the war, overtaking the previous" but doesn't that imply that previously immune people are no longer safe? (Also the theory doesn't seem to have much actual evidence)