Yup, and also we obviously have many more cases of flu recorded than cases of this virus so far, so the mortality rate can't really be compared so far (and I hope it doesn't spread as much as "regular" flu so we don't have to know for sure.)
You can't properly calculate the mortality rate or the case-fatality ratio until an epidemic is over. Mostly because an on-going epidemic involves a lot of ongoing cases where the outcome is, kind of obviously, uncertain.
Just so we're all singing from the same hymn sheet, in epidemiological terms:
- Mortality rate - the proportion of the general population (i.e. infected and uninfected alike) who become infected and die from a disease in an epidemic. Usually expressed as the number of deaths per 100,000.
- Case-fatality ratio - the proportion of people who have become infected who will die from a disease in an epidemic. Usually expressed as a percentage.
- R0 - the basic reproductive ratio - the number of other people that an infected person will infect in turn.
So, best estimates for Covid-19 at the time of writing:
- Mortality rate - none, the epidemic is still in progress.
- Case-fatality ratio - 2-3%. Estimates vary widely.
- R0 - 1.4-3.8
Yes, I agree, "You can't properly calculate the mortality rate or the 'case-fatality ratio' until an epidemic is over." You do not, however, wait "until the epidemic is over" to make decisions. If they are to be evidenced-based decisions, then they need to be based on the evidence that is available. I am not saying that you disagree with that or that you have said otherwise, I am emphasizing the point.
Take, for example, the graphs below (I have not attempted to validate the data):
from:https://www.popsci.com/story/health/covid-19-coronavirus-death-rate-by-age/ Source:CDCC Most recent data available as of March 5, 2020Infographic by Sara ChodoshThe need for a presumptive overall mortality rate is less compelling than looking at where the deaths have occurred, "so far" - at least for the over 50 crowd.
If you are trying to decide whether to close schools, for example, do you decide based on the observed overall mortality rate so far? I might add that the under 50 crowd is less likely to have the "responsibility" of deciding whether to close a school or not.
I like that you brought up the terms and this is not a counter-post to what you have said, it it just expressing a very difficult and practical matter. I am glad that I do not have to make such decisions, but I want to see them as evidenced-based.