"Your 3-5 years assumption is more egregious that the assumption of lost pathogenicity."
I'll go back and see if I can't find the article I was reading, but it stated that it would be 4.7 years until the planet resembled something akin to the way it looked in the summer of 2019.
"By 1920 numbers had fallen due to proportion of population infected and either immune or dead being high enough to squelch transmission. That state is the end goal for all public health responses."
Dude, if you're an advocate of lock-downs, the Spanish Flu is not the example you want to present.
This is important, so pay attention: There were no limits on human interaction during the Spanish Flu pandemic. It was because of this permitted interaction that the virus was able to spread, which eventually resulted in herd immunity. And it still took two years! Had they locked down hard back then...how long do you think it would have taken for herd immunity to develop? Would it have?
It wasn't vaccines that ended the Spanish Flu, it was naturally occurring herd immunity.
And here's another thing. The Spanish Flu was not like COVID. COVID kills old people with underlying conditions. People who likely aren't working, aren't traveling, and limited in human interaction. The Spanish Flu killed the very young and middle aged. People who would be interacting with many other people as a result of work, social life, whatever. SF killed something like 4% of all factory workers in the US. The "roaring 20's" are today viewed as the outcome of a generation that survived both war and a pandemic.