I don't know how the W.T. can use the Spanish Influenza as a tool to show end time predictions. There were many other plagues before this, and we're still here.
My findings on the Spanish Influenza...Reasons for large scale deaths.
First major global travel.
No medical history on this flu.
No medical injections to counter or give immunity to it.
Disease not isolated.
No world health organization at this time.
No quarantine measures were in place because of little known knowledge of treatments.
Outbrakes traced as far back as 412 B.C.
North American Indians.....
Diseases killed 90 percent of many Indian tribe populations, and substantially weakened others.
note: Keep in mind that populations were much lower in earlier times so the ratio of deaths must be taken into account.
1890 census... Only 200,000 Indians left. Wouldn't that be a better start of the "end times" prediction date?
How about the Black Plague, or Bubonic Plague? (1347 to 1351)
Was a bacteria spread by fleas, from rats. Small cities became ghost towns, large cities lost 1/2 to 2/3 rds. of thier population. Started in Constantinople, spread to Sicily, Sardinia, Corsica, Marseilles, then London, Ireland, Scandinavia, and central europe. . Disease made worse by crowded cities.
Reasons for spreading include..... Poor sanitary conditions, no quarantine measures even know about at that time. Enhanced by religious superstitions, ei; blaming plague as God's punishment to man.
But, as I said, we're still here.