Evaluating the effectiveness of social distancing interventions against COVID-19

Laura Matrajt; Tiffany Leung

We developed an age-structured susceptible-exposed-infectious-removed (SEIR) model to describe the transmission of COVID-19. We divided the population into ten age groups: 0-5, 6-9, 10-19, 20-29, 30-39, 40-49, 50-59, 60-69, 70-79, and > 80 years old (yo). We calibrated the model to the Seattle, WA metropolitan area and the age distribution of the population using census data [13] . Namely, for each age group, the population is divided into compartments: susceptible S, exposed E (those who have been infected but are not yet infectious), infectious I and removed R (Figure 1 ). Table 1 gives the parameters and ranges used in the model. Based on current estimates [14] that put less than one percent of the infections as asymptomatic, we considered only symptomatic infections. We used the contact matrix for six age groups computed by Wallinga et al. [15] and extend it to ten age groups. A full description of the model can be found in the Appendix. Using genomic epidemiology of the first two cases identified in the state of Washington, Bedford found that by the time that the second case was identified in Washington state, SARS-CoV-2 had been circulating locally for six weeks [16] . Hence, we considered January 21, 2020 (the day the first case was identified) to be the first day of our simulation.