Figure 1.

Model of social interactions and SARS-CoV-2 transmission and control

(A) Distribution of daily contacts made at home, work, school, and other settings in the BBC Pandemic dataset. (B) Examples of daily social contact patterns for four randomly selected individuals in the model. (C) Factors that influence whether an individual is isolated and whether contacts are successfully traced in the model (parameters presented in table 1). (D) Implementation of contact tracing in the model. The timeline shows a primary case with four daily contacts self-isolating either 1 or 3 days after onset of symptoms. We assumed the household contact to be the same person throughout, whereas other contacts are made independently. Had the primary case not been isolated, seven secondary cases would have occurred in this illustration (shown with circulations). For isolation 1 day after onset, four secondary infections were prevented immediately. Then seven contacts were potentially traceable, three of whom were infected. In this example, two infected contacts pre-isolation were successfully traced and quarantined (ie, one was missed), so overall the isolation-and-tracing control measure resulted in a 4 + 2=6 reduction in the effective reproduction number. A similar illustration is shown for isolation 3 days after onset. SARS-CoV-2=severe acute respiratory syndrome coronavirus 2.