Fig 1.

Model schematics of (A) COVID-19 health states and (B) close contact interactions between population subgroups in the pre-COVID era. In the model, susceptible individuals may become infected through interaction with infected individuals who may or may not be aware of their infection status. Infection has a pre-symptomatic phase in which an infected individual can transmit the infection to others. Individuals may become aware of their infection status through symptom-based surveillance, contact tracing, or routine testing of asymptomatic and mildly symptomatic individuals. Individuals aware of their infection status with mild or moderate symptoms isolate at home to reduce disease transmission. Some patients develop severe symptoms requiring hospitalization or critical symptoms requiring mechanical ventilation (MV) in an intensive care unit or renal replacement therapy (RRT). Patients receive medically indicated care unless resource demand exceeds capacity. When hospital capacity for a medically indicated resource has been reached, patients receive the next-best available care. The average number of contacts per day for the general population was estimated using an extrapolation of the 2008 POLYMOD data to a Canadian setting [10]. For university students, average contacts per day was estimated based on surveys in this population [11]. Average contacts per day for long-term care residents were estimated using a study in which residents and staff were equipped with RFID tags [12, 13].