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Statewide school closures were associated with a decline in COVID-19 cases and mortality from the disease, along with other non-pharmaceutical interventions, a population-based study found.

From March to May, school closure was associated with a 62% decrease in incidence of COVID-19 (adjusted relative change per week -62%, 95% CI -71% to -49%), and a 58% drop in COVID-19 mortality (adjusted relative change per week -58%, 95% CI -68% to -46%), reported Katherine Auger, MD, of Cincinnati Children's Hospital Medical Center in Ohio, and colleagues.

Moreover, these associations were largest in states with the lowest incidence of COVID-19 at the time of school closure compared with those with the highest cumulative incidence (-72% relative change in incidence vs -49% change in incidence, respectively), they wrote in

However, the authors noted an important caveat to their study: that a variety of non-pharmaceutical interventions, such as mask wearing and closing other non-essential businesses, took place virtually simultaneously, making it difficult to isolate the effects of any single intervention.

The debate over the scope of reopening schools this fall continues to rage, as medicine and politics overlap. Auger and colleagues noted prior research found an association between school closure and reduced transmission of viral respiratory illness, but added that states closed schools without evidence that school closings were effective in curbing the spread of SARS-CoV-2.

"Knowing whether school closure is effective in reducing infections is critical to reduce the negative effects of continued school closure on child health if school closure is ineffective," they wrote.

The authors performed an interrupted time series analysis of all 50 states from March 9 to May 7, allowing 6 weeks of data collection after school closures in each state. They included other non-pharmaceutical interventions as covariates, including closing non-essential businesses, such as restaurants and bars, and prohibiting large gatherings, based on the effective policy date, and a lag period that allowed these policy changes to occur. States were divided into quartiles based on COVID-19 cumulative incidence per 100,000 population at the time of school closures, all of which were closed beginning on March 13 to March 23.

School closures were associated with an estimated absolute difference of 423.9 cases per 100,000, and an estimated difference in mortality of 12.6 deaths per 100,000. When extrapolated to the U.S. population using mathematical modeling, the authors found school closures were estimated to be associated with 1.37 million fewer cases over a 26-day period, and 40,600 fewer deaths over a 16-day period.

Noting the "close proximity" of other non-pharmaceutical interventions other than school closures, by Julie Donohue, PhD, and Elizabeth Miller, MD, PhD, both of the University of Pittsburgh, said it is "difficult to disentangle the potential effect of each intervention."

Donohue and Miller also said the analysis does not explain how school closures affected viral transmission, writing, "Whether the estimated associations between school closures and COVID-19 outcomes derive from reducing contacts among children or among their parents and caregivers, who are also less mobile as a result, is not known."

They added there is also no way to know the "optimal duration, combination and sequence of non-pharmaceutical interventions, including school closures," which would have been easier to figure out if school closures happened after the other interventions were put in place.

The editorialists recommended a "precision public health approach" to any school reopenings this fall, including access to real-time data to "evaluate the effectiveness of specific approaches and adjust accordingly." They even suggested a specific role for clinicians.

"Health practitioners involved in caring for children should consider formal partnerships with their local schools to help guide reopening and offer micro-level adjustments based on available information," they wrote.

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