“Values ​​so constant for months, it’s strange”

As a member of the Corona working group at the Leopoldina National Academy, physicist Dirk Brockmann from the Institute for Theoretical Biology at Humboldt University Berlin has contributed a lot to the new statement “Establish effective rules for fall and winter”. Some consider experts like him great prophets, who can program and feed complex models of infection processes with algorithms and data. He himself is much more realistic and pragmatic.

Leopoldina’s new recommendations assume that the pandemic situation will intensify in autumn and winter and that the infection process may be more difficult to control. What do we have to expect exactly?

We cannot say that. Nobody knows, what we can say is: We have been in a kind of smoldering fire for six months. The number of cases has remained essentially constant for three months, but it is not disappearing either.

How great is the risk that the pandemic will flare up again like in Spain or France?

You can not say that. There are models that show different scenarios. In some the numbers are skyrocketing, in others not much is happening because people are watching the measurements. Of course, it will be different because, for example, it was mostly younger people who were recently infected, but it is particularly difficult to predict what that means at the moment. Because in Germany a level has stabilized with the number of cases in which the reproduction number R, often cited, barely oscillates around the critical value of 1. Such critical phenomena, when a system is currently pending a threshold value , have the property that they are difficult to predict in models.

What information are you missing to get more accurate forecasts?

We are dealing here with a system that has a high degree of feedback. How an epidemic spreads in the population is comparatively easy to describe mathematically. But it also happens that information spreads, politics reacts, people change their behavior based on their perception of risk. The behavior then changes the course of the pandemic and that in turn changes the behavior. These are inherently very difficult cycles to predict. Many think that our models make some kind of weather forecast. You can make short-term forecasts, but what goes beyond that is not serious. And for that they are not necessarily our models. We are not trying to explain what will happen in six weeks, but rather trying to identify what will happen when this or that changes. These are qualitative statements, but scientifically very valuable.

Will the number of cases remain stable?

We don’t know why the number of cases has been so constant for months. It is strange that an epidemic has such constant values ​​for months. It tends to spread or shrink, but conversations with international modelers have also revealed that it is difficult to explain. There is only speculation, maybe it could be due to the spatial heterogeneity in the country, the seasonality of the virus or completely different things. There is no mechanistic model that explains constancy.