Modelling studies suggest that school closure has its greatest benefits when schools are closed very early in an outbreak, ideally before 1% of the population falls ill.
模型研究提示，疫情发生较早时关闭学校带来的益处最大。理想的时机是在不足1%人口患病之前。
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Youngstown, a steel town, was devastated when its mills closed: over 30 years it lost more than half its population and thousands of jobs.