Figure 1: Model scheme. The 32 state variables are denoted by n + subscript. All pools other than the virus pool ( 𝑛 v i r ) and the dead-from-influenza pool ( 𝑛 d e d ) suffer from a natural mortality rate of μ (Table 1, where parameters are listed). Many categories (e.g., “Infected”) consist of sequential pools. The four infected pools all have (incubation) rate constants of 𝑘 i n f . Similarly, 𝑘 s i c applies to the four nonhospitalized clinically sick pools, 𝑘 h o s to the three hospitalized clinically sick pools, 𝑘 a s y to the seven asymptomatic pools, and 𝑘 d e l to the ten pools in the loss-of-immunity delay pipe. 𝑓 a s y and 𝑓 h o s are the fractions of the fluxes between 𝑛 i n f 1 and 𝑛 i n f 2 , and 𝑛 s i c 1 and 𝑛 s i c 2 , which are asymptomatic and hospitalized. 𝜇 s i c and 𝜇 h o s are the death rates (caused by flu) of the clinically sick and hospitalized pools.