Close all schools?

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Q: How about proactive school closures, before there are any infections associated with a school? Are they helpful?

A: Proactive school closures—closing schools before there’s a case there—have been shown to be one of the most powerful nonpharmaceutical interventions that we can deploy. Proactive school closures work like reactive school closures not just because they get the children, the little vectors, removed from circulation. It’s not just about keeping the kids safe. It’s keeping the whole community safe. When you close the schools, you reduce the mixing of the adults—parents dropping off at the school, the teachers being present. When you close the schools, you effectively require the parents to stay home.

There was a wonderful paper published that analyzed data regarding the Spanish flu in 1918, examining proactive versus reactive school closures. When did [regional] authorities close the schools relative to when the epidemic was spiking? What they found was that proactive school closing saved substantial numbers of lives.
St. Louis closed the schools about a day in advance of the epidemic spiking, for 143 days.
Pittsburgh closed 7 days after the peak and only for 53 days.
And the death rate for the epidemic in St. Louis was roughly one-third as high as in Pittsburgh.
These things work.

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From
https://www.sciencemag.org/news/2020/03/does-closing-schools-slow-spread-novel-coronavirus