Mobility data show a largely return to normal out-of-home activity levels - as in the previous summer. The general situation is unclear, especially because of the not exactly known protective effect of the vaccinations against the pure transmission of the delta variant. In the worst case, the infection, including infections of already immunized persons, will spread even faster than in autumn 2020. Fortunately, infections of already immunized persons rarely lead to severe courses; however, the possibly severe courses of non-immunized persons remain, which can still lead to considerable burdens for hospitals. Based on available data for the Berlin situation, we discuss some possible indicators of pandemic occurrence. In particular, total hospital occupancy (including general wards) seems to be a suitable indicator for Covid-19. Based on our ODE model, we quantify the effect of travel to high or low incidence countries. An important result is that returning individuals from high-incidence countries in principle increase the incidence in the home country, but this can be reversed by targeted testing followed by isolation if necessary, if only the compliance rate for this measure is sufficiently high. 

