Tracing DAY-ZERO and Forecasting the Fade out of the COVID-19 Outbreak in Lombardy, Italy: A Compartmental Modelling and Numerical Optimization Approach.

Lucia Russo; Cleo Anastassopoulou; Athanassios Tsakris; Gennaro Nicola Bifulco; Emilio Fortunato Campana; Gerardo Toraldo; Constantinos Siettos

Regarding the recovery period, in a study that is based on 55,924 laboratoryconfirmed cases, the WHO-China Joint Mission has reported a median time of 2 weeks from onset to clinical recovery for mild cases, and 3-6 weeks for severe or critical cases [18] . Based on the above, and on the fact that within the subset of case-patient (infector) having symptoms and a secondary case-patient having again symptoms. In our model, the 1 σ = 3 period refers to the period from exposure to the onset of the contagiousness. In this period, obviously there 165 are no symptoms. Thus, the serial interval in our model is 7 days (this is the average number of days in which an infectious becomes recovered and no longer transmits the disease). Importantly, there are studies (see e.g. Nushiura et al. [20] ) suggesting that a substantial proportion of secondary transmission may occur prior to illness onset. Thus, the 7 days period that we have taken as the 170 average period that an infectious person can transmit the disease before he/she recovers, reflects exactly this period; it refers to the serial interval for the cases that are asymptomatic and for cases with mild symptoms.