Time Delay Model for the Spread of Covid-19
In the classical models SIR and SEIR all model parameters are kept constant after they have been determined from the data. This is a serious drawback for the analysis of Covid-19 at this stage. Especially in order to analyze the effect of the lockdown actions and to be able to evaluate possible exit strategies, the model parameters must not be considered constant over time.
At the same time, an adequate model for the spread of Covid-19 must also take into account the fact that the effect of the actions occurs with a time delay. Therefore, the Fraunhofer ITWM has extended a classical SEIR model by time delay effects in order to be able to provide reliable spread predictions earlier than the classical models and thus enable the analysis of the actions. A further shortcoming of the classical models is that the dynamic of the epidemic is assumed to be homogenous across all regions and age groups. The Fraunhofer ITWM contrasts this assumption with cohorts, each with their own parameters and exchange coefficients. This also makes it possible to evaluate specialized actions, e.g. the opening of schools or relaxed contact restrictions in sparsely populated, rural regions.
Based on parameters adapted to publicly available case numbers, the ITWM research work around the scientists Dr. Jan Mohring and Dr. Raimund Wegener presents first predictions for the scenarios "herd immunity" and "eradication of the virus". In their results, they explain the two scenarios and use the basic reproduction rate to predict the duration and the chances of success of the scenarios.