Discussion
We conclude that the 4-week soft to moderate shutdown started on Nov 2 cannot on its own be expected to prevent a third, possibly even stronger wave of COVID-19. Repeated shutdown periods (with moderate to severe restrictions) could allow basic activities to be maintained, while keeping the COVID-19 waves under control. Maintaining the measures already partially introduced in October until spring of 2021 together with some of the measures announced on Oct 28, and possibly combined with short-term stronger restrictions, seem to promise the containment of the epidemic in Germany through the winter. Come spring, shifting of social activities to outdoors settings, possibly accompanied by availability of save and effective vaccines, may help suppressing the long winter outbreak.
We note that the observations above and simulations shown in Fig. 2 are based on mathematical models that, as a matter of principle, only describe a part of reality. In particular, reactions of the population to increasing case numbers (more cautious behavior, self-limitation of physical contacts) on the one hand and less than perfect compliance with officially mandated restrictions on the other hand may lead to significant deviations from theory. It is mathematically not possible, based on reported cases, to quantify the effects of any single intervention measure, as there have only been varying combinations of measures in the short history of COVID-19 control. Possibly the strongest limitation of mathematical modeling in the context of COVID-19 forecasts is that these are based on official case counts only, hence solely on detected cases. The unknown detection ratio, which is most likely fluctuating in dependence on new cases and testing capabilities, might significantly affect the outcome of model simulations [9]. In order to model the occupation rate of ICU beds, we assumed that the same standard for admission to and release from intensive care is uniformly applied over time. Changing this admission policy over time in reaction to higher demand may lead to lower ICU occupation than shown in the model. Finally, the presented model results cannot - and do not intend to - make any statements about possible economic or social effects of contact restrictions.