The Spanish flu came after the Great War, that's what made it so deadly. That and lack of medication, poor sanitation, hunger etc. which made people even more vulnerable. We have similar pathogens today, some if which mutated from the Spanish flu (Influenza type A). Also, flu is caused by a virus and this research is about antibiotic resistant bacteria.

The public health response was relatively ineffective in 1918 (influenza was not particularly well understood then), a similar virus would very likely not infect the same proportion of people as were infected then.

The proportion would probably also be reduced in at least 2 ways. The geographic extent would be smaller, and in areas where there were outbreaks, fewer people would be infected.

If there was a good vaccine match for the virus, even more so.

> The geographic extent would be smaller

This is definitely not my area, but as a lay person I've heard that because of the large increase in global travel, a dangerous flu strain could spread basically to basically every continent before we had time to meaningfully respond. Do you have reason to believe that isn't the case?

The 1918 pandemic also arose in a world without air travel. The geographic extent of any similar disease would not be smaller, it would be much larger and spread much quicker.