@MontereyJack,
Important as well, the virus that causes the disease, Sars-CoV-2, is a new pathogen in humans, meaning we are all immunologically naive to it.
The CFR of the 1918 flu is still being debated, mainly because there was then no reliable diagnostic test for flu, but the number usually quoted is 2.5%.
There are -why didn't coldjoint mention it? - two other flu pandemics that struck in the 20th century: the 1957 "Asian" flu, and the 1968 "Hong Kong" flu.
Both had CFRs much closer to 0.1%, and neither killed more than 3 million people at the most. Another major difference between the 1918 flu and Covid-19 is that the flu mainly affected those aged between 20 and 40, while Covid-19 mainly affects those over 60.
An interesting aside: one of the reasons the 1918 flu came to be known as the "Spanish" flu was because Spain was neutral in the war and didn’t censor its press - the US, Britain and France, all of which had the flu before Spain, kept it out of the newspapers at first to avoid damaging morale.
In the German Reich, for strategic reasons, it was not permitted to report on illnesses at the front. In the summer of 1918, however, German newspapers wrote about cases of influenza in the civilian sector. To avoid panic, it was spread that there was only one fatality for every 500 people who fell ill. The flu was at first called "Blitz catarrh" or "Flanders fever".