Why is COVID-19 mortality in Lombardy so high? Evidence from the simulation of a SEIHCR model

The standard SEIR model based on a parameterization consistent with the international evidence cannot explain the very high COVID-19 related mortality in Lombardy. This paper proposes an extension of the standard SEIR model that is capable of solving the puzzle. The SEIR model features exogenous mortality: once Susceptible individuals become first Exposed, and then Infected, they succumb with a given probability. The extended model inlcudes an Hospitlization process and the possibility that Hospitalized patients, who need to resort to Intensive Care Unit, cannot find availability because the ICU is saturated. This Constraint creates an additional increase in mortality, which is endogenous to the diffusion of the disease. The SEIHCR (Hstands for Hospitalization and C stands for Constraint) is capable of explaining the dynamics of COVID-19 related mortality in Lombardy with a paramerization consistent with the international evidence.