For those who haven't, the Wikipedia article on the pandemic of 1918 - which burned through the world with little intervention - is interesting.
https://en.m.wikipedia.org/wik...#CITEREFBillings1997
Also, when testing results are showing 20% positives it means we don't have a clue on the spread through the population. When positive results get to South Korea's level (about 1%), then we have a handle.