Because of its exponential nature, the current increase in incidences is worrisome. According to our model, this increase will be accelerated if schools open after the summer vacations without protective measures and if activities are shifted indoors in the fall due to low temperatures. The latter will also lead to an increase in hospital admissions (see Section 3 p. 2).

For most students, no immunization services will be available by the end of summer vacation without significant hurdles. To leave students the option of immunization through vaccination, both protective measures in schools and low incidence among adults are necessary until such offers is available. Otherwise, students are very likely to become immune by infection (see Section 3, p. 2).

We show with simulations that different subgroups have strong interdependencies: opening schools after summer vacation without protective measures results in a wave of infection among students, which also leads to a wave among adults. Conversely, a wave of infection among adults also leads to a wave of infection among students (see Section 4, p. 6).

Our simulations show that the infection dynamics in schools can be significantly reduced by the use of mechanical ventilation systems combined with the widespread use of rapid and/or PCR testing. With consistent implementation of these protective measures, school closures or alternate instruction are not necessary. However, the currently typical "2 rapid tests per week" are far from sufficient without additional measures (see Section 5, p. 7).

We use our mathematical model to show the impact of travel entry from different regions on the incidence here. We see that entry from virus-variant areas leads to a rapid spread of that variant here, whereas entrants from areas where the same variant is prevalent as here hardly influence the local incidence (for the time being) (cf. section 7, p. 11).
