Methods
The results shown here are based on simulations of a mathematical compartmental model of SEIR (susceptible-exposed-infected-recovered) type that in addition accounts for undetected and hospitalized cases and partitions the population into age classes. The compartments are summarized in Figure 1 and transitions between them are described by a system of ordinary differential equations comparable to what was proposed in [5]. Susceptible individuals become exposed by effective contact with an infectious individual. Exposed individuals progress through three stages, E1, E2, andE3, before onset of possible symptoms. Individuals in stage E3 are pre-symptomatic but already infectious. By testing and clinical diagnosis, both pre-symptomatic and unknown infectives can be detected. Detected or undetected diseased individuals can require hospitalization or even intensive care. By assumption, hospitalized and ICU patients are automatically reported as infectious, if not detected at an earlier stage. Hospitalized patients can reach a critical state and be relocated to ICU. All infected persons will eventually recover or might die from the disease. Importantly, individuals having recovered from undetected infection will never show up in official case counts. Individuals in any of the age groups considered here (juveniles: age 0-14y; adult: 15-59; senior: 60+) can be in any of the above states. Age classes evolve in parallel and are coupled to one another by contact rates among individuals. Demographics are neglected, meaning that besides fatalities caused by the disease, no individuals enter or leave the population. The model is calibrated on reported case counts [10], hospitalizations and ICU occupation as daily reported by the Robert Koch Institute [2], following methods previously adopted in [5].