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In order to make predictions, it is necessary in the current situation to make assumptions about the behaviour of the infectious agent. These are based on data on the occurrence of the infection observed to date and become increasingly predictable the longer the pandemic lasts. Published data speak for themselves

for the fact that SARS-CoV-2 infections are mild to moderate in most cases, while 2-5%

of the cases require treatment in the intensive care unit. Risk groups for severe courses of disease are all older people [1, 2] and people with previous illnesses. Tobacco consumption also appears to be a risk factor or an unfavorable course of disease [1]. Children usually have a very mild course, but can still transmit the infection.

**An important parameter for modelling the spread of infection is the baseline reproduction rate (R0). This indicates the average number of people infected by an infected person when no infection control measures are carried out and there is no immunity in the population (in further course of propagation this changes and one speaks of the effective reproduction number).**For SARS-CoV-2, R0 is estimated at 2-3 [3]. Imagine a scenario in which NO specific control measures are implemented and no spontaneous changes in behavior occur, would under the assumption that all persons develop immune protection after an infection in the course of the outbreak will infect about 50-70% of the population, initially at an exponentially increasing rate. If the epidemic were to proceed unchecked according to this scenario, the peak of the outbreak would be (maximum number of infected persons) already in summer 2020 (Fig. 1).

Fig. 1: Temporal course of the epidemic for different basic reproduction numbers (R0) / effective reproduction numbers. This represents the impact of control measures through different reproduction numbers after the introduction of the measures on COVID-19 case numbers. On the horizontal axis the time and on the vertical axis the number of persons who are infected at any one time (panel A) or need treatment in an intensive care unit (panel B). For example, on day 50 at a reproduction count of 2.5 5,687,270 infected persons (Panel A), at a reproduction count of 2 would result in 1,140,233 persons requiring intensive care on day 100. The different curves in the graph also show slower progression of the epidemic, i.e. they show what happens when the reproduction count is reduced by the introduction of control measures, as currently in Germany has already partially implemented the directive. The great danger of an unimpeded outbreak is that in a short period of time a very large number of patients will require treatment at intensive care units and the health care system would very quickly be overtaxed by this. Currently, the health care system in Germany has about 30,000 intensive care beds; most of these are continuously needed for patients who are subject to intensive care regardless of the current COVID-19 problem. When interpreting the model results, it is noticeable that even moderately slowed progression of the infection spread would lead to decompensation of the health care system. Only a Reduction of the effective reproduction number in the range of 1 to 1.2 would result in a course within the existing capacities of the health system.

A control of the propagation speed into this narrow range seems practically inconceivable, because even a small increase of the reproductive rate would lead to the health system being overtaxed.

Another possible strategy would be to reduce the effective reproductive rate below 1 and thereby to contain the epidemic. The decisive measure here, in addition to the already established infection control strategies (e.g. reduction of the probability of transmission through consistent hand hygiene, isolation of infected persons, quarantine of contact persons) also in the entire population to achieve a restriction of social contacts to the bare minimum. Should it be thus succeed in containing the spread of infection in Germany until there are no new cases, would have to continue to prevent the re-introduction of the infection, or individual cases that occur would have to be quickly identified and isolated by means of a broad-based testing strategy.