We do not know the mortality rate with any precision at this point and early estimates place it far higher than 0.7%.
Let’s be neither alarmist nor complacent, but above all get our facts right and avoid spreading misleading information.
As with the flu, mortality is highest in older people, and the immunocompromised.
[1] https://www.who.int/docs/default-source/coronaviruse/who-chi...
> This makes a lot of sense as the earliest numbers were based only on people presenting severe symptoms, and huge quantities of people with nCoV are completely and totally asymptomatic.
Isn't another possible explanation that it simply takes very sick people a few weeks to die from it, so if you start counting a week farther back then the confirmed-then-died rate will be higher? (Due to undercounting of people who are going to die from it but haven't yet.)
We need to be careful about what exactly the WHO is reporting. In this case, they are reporting estimates of the crude fatality rate defined as deaths / total cases. This will equal the mortality rate once the outbreak is over, but has limited use during the outbreak as they call out in footnote:
> The Joint Mission acknowledges the known challenges and biases of reporting crude CFR early in an epidemic.
During the outbreak, a better but still imperfect estimate is deaths / settled cases where settled cases is the sum of deaths and recoveries. [1]
> huge quantities of people with nCoV are completely and totally asymptomatic.
From 72.314 cases, as of February 11, 2020, only 889 asymptomatic cases (1%).
> Nevertheless, all CFRs still need to be interpreted with caution and more research is required.
Like the cruise ships:
> The ministry has tested 4,061 people so far, of which 705 were positive, including 392 people who were asymptomatic.
So seems your estimate of "huge numbers of asymptomatic" is not far from the mark. Apologies. See also:
> Asymptomatic infection has been reported, but the majority of the relatively rare cases who are asymptomatic on the date of identification/report [due to contact testing] went on to develop disease. The proportion of truly asymptomatic infections is unclear but appears to be relatively rare and does not appear to be a major driver of transmission.
https://www.who.int/docs/default-source/coronaviruse/who-chi...
Reasons behind this might be either institutional or purely statistical that is it might be possible that each country can keep alive at least certain number of critical patients and starts to fail when certain number is exceeded and it is possible that smaller number of patients are not representative enough and do not contain high risk patients (elderly, people with other chronic illness etc).
Edit: Diamond Princess is not representative because people have been evacuated and are now counted under countries statistics https://www.bloomberg.com/news/articles/2020-03-01/man-dies-...
From what I've read (see below), the current consensus is that China is under-reporting total infected, possibly by an order of magnitude. China also made several missteps in their initial and ongoing response that is likely increasing their mortality rate, especially in Wuhan and surrounding Hubei. Worldwide, there certainly are and will be people who are infected but are asymptomatic, and don't even know (and of course aren't being counted at all).
I would expect that the mortality rate outside China is -- and will stay -- sub-1%, unless it mutates and becomes more deadly, or if health services eventually become overwhelmed due to quick spread. Analysis of primary data seems to indicate that even non-Hubei China has a mortality rate around 0.7%; Hubei's mortality rate is skewing the total upward by a lot. Rest-of-world looks to be around 0.6% so far.
https://www.cnn.com/2020/02/19/health/coronavirus-china-sars...
https://www.bmj.com/content/368/bmj.m606
https://github.com/CSSEGISandData/COVID-19 (primary data, which links to some analysis and visualizations)
Reasons behind this might be either institutional or purely statistical that is it might be possible that each country can keep alive at least certain number of critical patients and starts to fail when certain number is exceeded and it is possible that smaller number of patients are not representative enough and do not contain high risk patients (elderly, people with other chronic illness etc).
If you look at the recent data then when number of patients approaches 100 then mortality (CFR) exceeds 2%. Only exception seems to be South-Korea. Diamond Princess is not representative because patients are now evacuated and counted under their countries statistics.