Figure 1. Schematic representation of the model structure. Black boxes represent infectious stages and arrows indicate that persons in these populations are allowed to fly. A) Severe acute respiratory syndrome. Persons with latent infections are not infectious, and all infectious persons are symptomatic and prevented from traveling. B) Pandemic influenza. Persons with latent infections are infectious, and a proportion (1 – s) of infectious persons are asymptomatic and allowed to travel (indicated by the dotted arrows). The size of the arrows indicates that the persons in the high-frequency flier group have a higher probability of flying per day.
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