We've come a long way from a medical standpoint since the Spanish Flu though. Medical Care was absolutely horrid back then. They had a shortage of everything. Hell, even their quarantine ability was probably abysmal back then. If the Spanish Flu happened today, the mortality rate would probably be closer to 1%
Transmission back then was much slower due to travel methods. No international flights to speak of, much lower population densities, no interstate highways, etc. Yes, health care and communication and science are more advanced. But so are means and methods of transmittal and, for various reasons, we can't seem to even figure out how to make a test to see who is sick in any kind of reasonable time frame.