https://www.technologyreview.com/202...wn-in-germany/
Germany is one of the first to do a wide spread survey of the general population using antibody tests to determine how much of the population has contracted the disease. They tested 1,000 residents and found 2% had an active infection and 14% had antibodies showing that they were immune. From this study they were able to estimate a death rate of .37%.
The mortality rate for the flu is .1%. It's still a significant jump from the flu and the hospitalization rate has been enough to overload hospitals around the world.