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If you should get ill, there are two options. You will either be cured and survive, or you will die. When the disease is over and everybody is either cured or dead, we can talk about an absolute mortality, defined as (no. of dead) / (no. of dead+ no. of recovered). However, during an epidemic it is not always easy to figure out what the absolute mortality will be. Calculating the mortality as (no. of dead) / (no. of dead+ no. of recovered) may still make some sense, and we will therefore call this figure the actual mortality. Where absolute mortality is the end-value of the actual mortality, when the disease is over, and everybody is either cured or dead.
But because Corona-19 is a new virus, there has been some uncertainty of the absolute mortality of this virus, simply because it is a lot easier for people to die than to become cured. On 13th of March, for example, only 1 has been reported to be cured in Belgium, while 3 people had died, which apparently gives an actual mortality rate of 33%. But since there are 395 who are still ill in Belgium, this picture is expected to change quickly. So, because actual mortality can give a very high and misleading number, to begin with, one usually relies on other figures, such as the case fatality rate (CFR). This is the number of deaths in relation to the total number of infected. In Belgium on the 13th of March, the total number of infected people is 399. The CFR can then be calculated as 3 dead out of 399 infected, which gives about 0.7% in CFR.
Where the actual mortality rate to start with may give a too high a figure, the CFR does thus give a too low a figure. But it is nevertheless the CFR which is usually referred to by scientists and thus also by the media. For Covid-19, the CFR has been around 2% until mid-February, where it then began to rise, with the CFR by the 14th of March estimated to be 4.34%. The reason for this is that CFR depends on how quickly the disease spreads and will only yield a value that is identical to absolute mortality when all disease cases are concluded. Using the CFR as a guideline can, therefore, be problematic, which for example can be illustrated by calculating the mortality rate for a disease that kills everybody after 30 days and which spreads like Covid-19. Initially, the CFR would be very low since it takes 30 days for the patient to die. But over time, the CFR will stabilize at a level that will depend on how quickly the infection spreads. Thus, with figures for Covid-19, a virus that has a mortality rate of 100% after 30 days (all will die after 30 days) will have a CFR rate of about 33% (at least with ourdata for the 13th of March). Using case fatality rate as a guideline can thus be highly misleading. Still, in many scenarios, it can be a better guideline to start with than absolute mortality, until the infection rate has stabilized.
However, both the CFR and the absolute mortality will depend on the data available. Using the raw data may therefore give a false impression of exactly how deadly the disease is. We will for instance notice that on the 23th of March, Germany has registered 29,056 cases, 118 death and 422 has recovered. This gives a CFR of 0.4% and actual mortality of 21.8%. The difference between CFR and the absolute mortality clearly illustrates that both figures are very wrong. When everything is over, the two numbers will be alike, so the true number will lie somewhere in between. The reason for the faulty figures is mostly because the disease has far from reached its full potential yet. Italy is a few weeks ahead of Germany and has the 23th March got 63,927 total cases, 6,077 dead and 7,432 have recovered. That gives a CFR of 9.5% and 45.0% in absolute mortality. This illustrates another issue by using raw data. Probably only the severe, hospitalized cases are taken into account for in Italy, and this will, of course, give a very high mortality.
To figure out how deadly the disease is, we will have to look for statistical data which are fairly accurate. The Chinese are desperately trying to wipe out the disease totally from China and has therefore need to know fairly accurate how many cases there are. And the 23th of March China has 81,093 total cases, 3,270 dead and 72,703 recovered. This gives a CFR of 4.0% and an absolute mortality of 4.3%. Again, when all cases have been resolved the two numbers has to be alike, so the true number must be somewhere in between.
Another detailis, thatit is known that not all which are infected do get symptoms. And since the Chinese primarily has only tested those which have symptoms, the incidence fatality rate (the death of all which getthe disease) is therefore even lower. It is believed that about half of those which have the disease will get symptoms, which means that the incidence fatality rate of Covid-19 is (most likely) slightly above 2.0%. This figure do also fit with what the Chinese claimed was the mortality rate of the disease, when they made a very large survey in the middle of January.
If we want to know how many people this disease potentially can kill, if it went loose freely, thenwe will have to assume that about 60% if the total population of earth will be infected by the disease. The reason for this is that as recovered people are supposed to get immune, they will not spread the disease, and when about 60% of the population is immune the disease will therefore eventually stop spreading by itself.
The population of Earth is of about 7,770,000,000 people, 60% of that is 4,662,000,000. Assuming that about 2% will die, will then give about 93,240.000 dead people in total. And please note, that this number is when the government is “just” trying to slow the disease down without stopping it. Because, if the disease is allowed to spread then the hospitals will not be able to handle the diseased people properly. It is estimated that about 5% of all which are infected by the disease will be serious ill. We will here assume that it implies that the patient won’t survive without a respirator. So, if there are no respirators available the mortality rate will therefore increase from 2% to 5%. The worst-case scenario is therefore actually that 233 million people will die. But since the societies are working on slowing down the disease, we may therefore “only” face about 93 million deaths.
However, people don’t have to die. The Chinese has proven that it is possible to stop the disease. As a matter of fact, they have almost eliminated it. The city Vò in Italy has also done it. The correct way to do it is to test everybody which has even small symptoms, and then test everybody this person has been in contact to, until the chain is found and eliminated. This goes on for everybody which have symptoms, and the disease can in principle be eliminated within weeks – if the necessary resources are available.