Widespread testing, case isolation and contact tracing may allow safe school reopening with continued moderate physical distancing: a modeling analysis of King County, WA data

Background In late March 2020, a "Stay Home, Stay Healthy" order was issued in Washington State in response to the COVID-19 pandemic. On May 1, a 4-phase reopening plan began. If implemented without interruptions, all types of public interactions were planned to resume by July 15. We investigated whether adjunctive prevention strategies would allow less restrictive physical distancing to avoid second epidemic waves and secure safe school reopening. Methods We developed a mathematical model, stratifying the population by age (0-19 years, 20-49 years, 50-69 years, and 70+ years), infection status (susceptible, exposed, asymptomatic, pre-symptomatic, symptomatic, recovered) and treatment status (undiagnosed, diagnosed, hospitalized) to project SARS-CoV-2 transmission during and after the reopening period. The model was parameterized with demographic and contact data from King County, WA and calibrated to confirmed cases, deaths (overall and by age) and epidemic peak timing. Adjunctive prevention interventions were simulated assuming different levels of pre-COVID physical interactions (pC_PI) restored. We made several predictions related to adjunctive interventions or increased pC_PI. Results The best model fit estimated ~35% pC_PI under lockdown. Gradually restoring 75% pC_PI for all age groups between May 15-July 15 resulted in ~350 daily deaths by early September 2020. Maintaining less than 45% pC_PI was required with current testing practices to ensure low levels of daily infections and deaths. If widespread community transmission persisted, isolating the elderly does not lower daily death rates significantly. Increased testing, isolation of symptomatic infections, and contact tracing permitted 60% pC_PI without significant increases in daily deaths before September, although this strategy may not be sufficient to eliminate community transmission. This combination strategy also allowed opening of schools with <15 daily deaths. Inpatient antiviral treatment reduces deaths significantly without lowering cases or hospitalizations. Conclusions We predict that widespread implementation of "test and isolate" policy alone is insufficient to prevent the rapid re-emergence of SARS CoV-2 without moderate physical distancing. However, widespread testing, contact tracing and case isolation would allow relaxation of physical distancing, as well as opening of schools, without a surge in local cases and deaths.