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].