The Corona epidemic seems out of control to. Mathematical models are helpful in order to cope with the Situation? With mathematical models we try to estimate how quickly the epidemic is spreading at the moment. In the ideal case to also evaluate the extent to which measures have been taken, have an impact on the spread.
What you need to know about a Virus such as Sars-CoV-2, to understand its spread? there are two different approaches. In one approach, one needs to know how many cases of disease it was which is the time in which regions. That would be the classic epidemiology. On the basis of these cases can then be used to extrapolate how the epidemic is evolving, if not taken precautions.
to do This you need cases, therefore, good information about the number. Exactly. At the outbreak of the Corona-epidemic in China, and also in Italy, the data situation, however, was quite thin. We can count the cases when we know of an outbreak, and that we will not see all the cases. This limits the accuracy of the analysis.
keep track of the epidemic on the basis of genetic information of the Virus. This is the second method. We use genomic sequence data of the Virus from different patients. If this is a random sample from the entire epidemic is, you can calculate begin using the gene sequences, how quickly the Virus is spreading.
The mathematician Tanja Stadler is a Professor at the Department of Biosystems Science and Engineering at ETH. They developed methods to calculate the spread of Virus epidemics.
How is this possible? The Virus is constantly changing due to mutations. When the virus genome of two patients are very similar, have you recently separated or both have been infected recently by a third Person. The virus genome of two patients differ significantly from each other, the two patients in the transmission chain of each other. So we are creating a family tree of the viruses, we can interpret as a transmission tree.
And hence the propagation speed calculated? Yes. From Italy we currently have 20 genome sequences. Although this is a small sample of the Thousands of people infected, we can determine with statistical methods, the velocity of propagation. The corresponding data we have from the Region in Wuhan, China.
And? We see no significant difference between the velocity of propagation in Wuhan and in Italy prior to the quarantine measures. Say: Without measures the speed of propagation in both places seems to be about the same.
This means: exponentially rising? Exactly. We calculate the so-called reproduction number. It indicates how many people are infected, an infected Person on average. If the reproduction number is greater than one, the epidemic will increase exponentially. Specifically, we obtained values for the reproduction number of two to three and a half, both for Wuhan, as well as for Italy.
It doesn’t sound so bad, if one Person infects two or three people. The annual flu has a reproductive number of about 1.3. The Corona epidemic spreads significantly faster. This shows that a very far-reaching health policy measures must be taken to press the reproduction number to below one. Only then will the epidemic is declining.
you Can estimate on the basis of the models, what to wash regular hands, quarantine, or the prohibition of some of the larger events really brings? basically, we can apply the same method that we use to determine the speed of propagation in the early days of the epidemic, only after the measures taken. Then, the possible changes in the reproduction number gives us a clue to the effectiveness of the measures.
How much is the drastic quarantine has brought in Wuhan? The quarantine has slowed the spread of the epidemic, for sure. This is at the present time is also very important, in order to prevent an Overload of the health systems. How much, exactly, the big has brought-scale quarantine, can’t we say with our methods but. The Problem is that we after the Start of the quarantine in the city of Wuhan on 23. January have extremely little data. The quarantine was so strict that hardly any of the biological samples were to more. The hope is that we will now get from Italy, so after the closure, more data.
How fast can you type of policy Feedback on whether measures are effective? We can analyze the data in near real time and make forecasts. In the sense of the Corona epidemic is unprecedented. In the case of previous epidemics, this was not conceivable. Since it has many weeks, if not months it took the Genetic data templates.
In Switzerland are prohibited for more than a week of events with over 1000 people. You can see there’s already an effect? In Switzerland we have only a few days ago, an uncontrolled course of the epidemic. Therefore, we need a few more days until we have enough genomic sequence data from patients, to calculate the current velocity of propagation.
it Is expected that the development in Switzerland differs from those in China or Italy? Italy and Wuhan are culturally and patterns of behaviour is certainly very different. Nevertheless, we see that without counter-measures, a similar velocity of propagation. Therefore, it is expected that the reproduction number is likely to be in Switzerland, also between two and three and a half, if no measures would be taken.
Supposedly, the number of unnoticed infections is very high. Were you able to determine the number of unreported cases? From the genetic data, we can calculate the total number of infected persons. For Wuhan, we have made the. At the beginning of the quarantine on may 23. January there was not even 600 confirmed cases. Our genetic analysis suggests that there was at this time a total of between 4000 and 19’000 cases. This means that the number of unreported cases is extremely high. For Italy, our estimates are extremely uncertain.
If the number of unreported cases is so high, then the mortality is lower than previously feared? Not necessarily. Also, the previous assessments of mortality have taken into account the unreported cases. The evidence suggests that the death rate in the range of one percent lies. But how high it actually is, we can’t say due to the data situation with safety.
rumor has it, the origin of the epidemic in Europe, sun in Bavaria. Can you confirm that due to the virus family tree? The genomic sequence data allow us to test the various hypotheses. You can think of it this way: If the pedigree of the Italian epidemic is part of the family tree of the Chinese epidemic, and the pedigree of the Bavarian epidemic is another part of the Chinese family tree, then this suggests that the Chinese Virus is directly passes to Italy, and directly to Bavaria. Conversely, if the family trees of Italy and Bavaria are almost identical and in many Chinese gene sequences are embedded, then this suggests that there is a direct Link between Bavaria and Italy. At the moment but we need more sequences from China, to the descent conditions in Europe clearly determine.
What should Switzerland do, in your view, in order to curb the epidemic? to have Around zero Transfers, would have to be isolated each Person. This is of course not feasible. So you have to Use in this case, the Federal office of public health, supported by ethicists, epidemiologists, and mathematicians, a cost statement to make: If we close now, schools, public transport shut down, or regions of dense make, then, is to reduce the number of new Infections to a certain degree. But: Is the reduction of the spread in Relation to the costs? To decide that, ultimately, is the task of politics.
Created: 10.03.2020, 15:13 PM
