How deadly is the coronavirus? A lower bound

For this estimate I will look at two of the world's most affected regions: Lombardy and Wuhan and use the data available today.

In Wuhan, the infection is over, for now, with 3000 deaths. The city has 10 million people. If everyone was infected, the death rate would have been 0.03%. If 60% of the population was infected, the death rate would be 0.05%. If the quarantine measures taken were successful and fewer people were infected, we should see a new wave of infections once life is back to normal.

In Lombardy, 2000 died so far, and there is no sign the pandemic has passed its peak. If all Lombardy residents (10 million people) were infected, a death toll of 2000 would mean the mortality of the virus is 0.02%. That's like swine flu. Sure, this is only a lower bound. The mortality is certainly higher. 

OK, so how many were tested? Lombardy has conducted 52244  tests -- ONLY about 0.5% of their population. Of those, 19844 tests were positive. That means 40% of the people tested had the coronavirus. IF we assume the people we didn't test have the same chance to be infected as the people we did test, we'd have 4 million infections at the moment with a death rate of 0.05%. 

We do know they were thrifty with the tests and tested primarily critical cases or people who met positive carriers. Even so, it is expected that the population they don't test to be less infected than those tested. However, it is believed that 70% of the cases are asymptomatic or quasi-symptomatic. Data from China suggests that 80.7% of their cases were mild, and less than 5% of the cases were critical. 

In the Italian town of Vo, they tested the whole population of 3000 people and detected 89 positive cases -- all asymptomatic patients -- BEFORE the first symptomatic case. So, if we take this as a benchmark, we assume that for every symptomatic patient, one has 100 mild or asymptomatic cases. For the 20 000 positive, symptomatic cases we have today we would have had 2 million residents infected that are quasi-symptomatic or asymptomatic in Lombardy, which would bring the death rate to 0.1%.  Now, Valeriu's plots show that the dead double about every 3 days.  The number of affected people should double at roughly the same rate. This means that the whole populations should be infected in a week or so if this lower bound were true and if the quarantine is ineffective. The total death toll would then be less scary -- somewhere between 5000 and 10000 people.

How does this compare with my guess of 0.2%?

My 0.2% guess for Lombardy's population of 10 000 000, would mean 10 000 - 20 000 deaths. For the 2000 people who died so far, we'd need one million to have been infected a few days ago. That would probably have increased to a few million by now -- already a good fraction of the total population of 10 million. If this is right, the pandemic should reach its peak in the next few days. 

If 0.2% of the people die, about one million people should have been infected a few days ago. Depending on how well the quarantine works, that number might have increased slower or faster. Sooner rather than later, however, it will have to stop as the pandemic runs out of people. 

Thus based on my 0.2% guess, I conjecture the following 

-- the quarantine in Lombardy does not prevent infection. It will however spread the peak of the pandemic and make it easier for hospitals to handle the patients. In a few days, most people would have been infected and in another few days, the pandemic will stop. By April 20, there will be no Coronavirus in Lombardy. Sure, isolated infections like in Wuhan today will still take place. 

-- Lombardy will NOT go beyond 20 000 deaths. 

-- The rest of Italy and will follow the same path, a few weeks behind. Southern provinces should have it easier with the arrival of summer weather. 

I hope my lower bound is truer than my guess because 20 000 deaths is still a lot. Either way, we should probably see the death rate plunge below the average of previous years during the months to come. 

The overall mortality will be similar in the rest of Europe. That means we'll see in Germany what we see in Italy now. So, by the end of March or in the first days of April, there should be over 3000 Coronavirus deaths in Germany as well.