We live in a very different earth now. The Spanish flu virus criss-crossed the globe in a mere 3 years, from January of 1918 to December of 1920. At the end claiming an unknown number of victims. The low estimate is 17 million deaths, and the high estimate being 50 million.
While the Spanish flu viral pandemic took place in a post-industrial world, one needs to consider what the most advanced aircraft at the time looked like.

That is not a passenger jet by any stretch. 1919 cities had nobody waiting in line to board at an airport takeoff gate. No people were squashed together in subway cars after a baseball game let out. A "large concert venue"? What's that? There were no regular television shows at that time, and no live audiences daily sardined into the seats.

Some are suggesting COVID-19 will claim 600,000 lives by summer, just in the United States. That number is often quoted as being the worst-case scenario for the continental 48. Chinese media is suggesting that the virus has already "run its course" in mainland China.