We consider the interaction of two measures: contact tracing and school openings. In the simulations, we observe an unstable situation with low infection rates, which can easily get out of control. In our simulations, complete opening of the schools after the summer holidays causes a considerable increase in the incidence of infection; an additional short-term opening from June 8 to 24, however, would have a relatively small additional infection effect.

In order to keep the infection under control, it is essential in our simulations that the capacities for contact tracing must be sufficient under all circumstances. Flexible personnel, as is already being provided, must be available in sufficient numbers under all circumstances and, if necessary, allocated where they are needed. Under these circumstances, the "manual" approach of the health authorities seems to be sufficient; an app, if widely used, would perhaps save costs, but does not seem absolutely necessary.

If this can be guaranteed, then opening schools seems feasible according to our simulations. However, the pressure on the overall situation would certainly be reduced if this were to be done only "partially", e.g. shift operation, partial electronic teaching, and/or significantly fewer people per room. Distance rules, frequent ventilation, etc. are part of our basic assumptions anyway.
