Figure 1. Comparing observed ILI incidence and model simulations.
a Weekly ILI incidence as reported to the surveillance system (green) and weekly incidence simulated by a “simple” SIR model (blue). Sub-panel shows the same curves in a logarithmic scale. Parameter values assumed in the simulation are: the generation time 
days [48]–[50] and 
, according to a serological survey on the Italian population [47]. Parameter values estimated via model fit are: 
, 
and 
. b Weekly ILI incidence as reported to the surveillance system (green) and weekly incidence simulated by a SIR model assuming a time-dependent transmission rate (blue). Sub-panel shows the same curves in a logarithmic scale. Assumed parameters are: 
days and 
. Values of the fitted parameters are: 
, 
, 
for weeks 38–41.58 and 
for weeks 41.58–51. c Weekly ILI incidence as reported to the surveillance system (green) and weekly incidence simulated by the proposed model (red). Sub-panel shows the same curves in a logarithmic scale. Assumed parameters are: 
days, 
, 
and 
. The values of the fitted parameters are: 
, 
, 
, 
, 
, 
and 
. In addition, the estimates of the reporting factor 
as obtained by fitting the three models and reported in a, b and c (namely, 17.4%, 16.7% and 16.9%, respectively) are in good agreement with the range 18%–20.2% estimated in [30].