Study population and setting
Investigators aggregated confirmed and probable COVID-19 cases and deaths between March 9 and May 7, 2020, at the state level. Changes in daily cumulative COVID-19 incidence (total cases per 1,000 persons) and mortality (COVID-19 deaths per 1,000 persons) were compared at the state level, before and after the closure of primary and secondary schools (March 13 to 23, 2020) in each state. The timing of other non-pharmaceutical interventions (e.g., stay-at-home orders, business closures) were adjusted for in statistical models.
Summary of Main Findings
Following school closures, significant reductions in both COVID-19 incidence (–62% per week) and mortality (–58% per week) were observed. After collapsing daily COVID-19 incidence estimates before school closings into four groups, reductions in COVID-19 incidence and mortality were greatest in states with the lowest COVID-19 incidence (median: 0.48 cases/100,000 persons) at the time of school closure (incidence: –72% per week; deaths: –63% per week) compared to states in the highest COVID-19 incidence quartile (median: 3.30 cases/100,000 persons), where weekly reductions in incidence and mortality relative to the prior week were –49% and –53%, respectively.
Investigators modeled a policy interruption (i.e., school closures) in time-series data available for all states in the country to examine the associations between school closure and COVID-19 transmission/mortality. Inclusion of other variables potentially associated with COVID-19 incidence and mortality (i.e., timing of other non-pharmaceutical interventions, COVID-19 testing volume per 1,000 residents, nursing home residents per 1,000 residents, demographic composition of the state population) helped facilitate attribution of observed outcomes to the primary exposure of interest, school closures.
The ecological nature of the analysis, which captures data aggregated to the state level, raises questions about unaddressed factors, like travel and mobility, or other non-pharmaceutical interventions driving incidence and mortality differences. Attribution of COVID-19 incidence and mortality reductions to school closures alone is challenging given the assumptions required regarding the timing lags (such as time from exposure to symptom onset) and the multitude of other interventions enacted during similar time frames. There was also little variation in the timing of school closures across states. Lastly, heterogeneities in States’ testing capacities and variability in testing accessibility between March to May could bias incidence and mortality estimates derived from the analysis.
This is among the first studies to quantify the independent effect of school closures on COVID-19 incidence and mortality in the United States.
This review was posted on: 14 August 2020