What do we already know?
School closures in Washington State were announced on March 12
th
, 2020 and have contributed to
reducing transmission of COVID-19. However, there remains uncertainty around the impact of school
reopenings on overall transmission. Schools across the state (and nation) are currently considering
strategies for reopening in the fall, including the use of cloth face coverings, physical distancing in
schools, daily syndromic screening, and classroom or school cohorting.
What does this report add?
We applied our agent-based model, Covasim, to simulate specific strategies for school reopenings as
well as changing transmission at workplaces and in the community. We calibrated the model to King
County data provided by the Washington State Department of Health, including daily counts of the
number of tests, diagnoses and deaths in 10-year age bins until June 15
th
. While we fit the epidemic
data well, we do not capture the more recent increase in cases that have occurred subsequent to this
period.
We compared six alternative strategies for school reopening, including changes in the contact
structure of schools, the usage of face masks and other non-pharmaceutical interventions (NPIs), and
the implementation of screening, testing and contact tracing of students and teachers. We found that
school reopenings with no countermeasures may lead to a doubling of the COVID attack rate in the
population over the first three months of the school year, but that a combination of mask usage,
physical distancing, hygiene measures, classroom cohorting, and symptomatic screening, testing and
tracing of students and teachers may be able to effectively reduce or even mitigate epidemic spread,
depending upon the level of community transmission in the model.
For example, if the workplace and community return to 70% of pre-COVID mobility by the time
schools reopen, which we estimate represents a five percentage point increase from activity in
mid-June, with ongoing testing and contact tracing, the use of masks, physical distancing,
appropriate hygiene measures, classroom cohorting, and symptomatic screening in schools may be
able to reduce the community-wide effective reproductive number to 1. This strategy would use 70
diagnostic COVID tests per 1,000 students over the first three months of the school term...
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