Learning and education are two of the biggest world issues of the current pandemic. Unfortunately, it is seen in this work that, due to the length of the incubation period of Covid-19, full opening of schools in the Fall of 2020 seems to be impractical unless the spread of the virus is completely under control in the surrounding region (e.g. with fewer than 5 active cases every million people).

In order to support the possibility of some in-person learning, we model the diffusion of the epidemic within each single school by an SEAIR model with an external source of infection and a suitable loss function, and then evaluate sustainable opening plans. It turns out that blended models, with almost periodic alternations of in-class and remote teaching days or weeks, are generally (close to) optimal. In a prototypical example, the optimal strategy prescribes a school opening of 90 days out of 200 with the number of Covid-19 cases among the individuals related to the school increasing by about 67% with respect to no opening, instead of the about 200% increase that would have been a consequence of full opening. As clinical fraction is low in children, these solutions could lead to very few or no symptomatic cases within the school during the whole school year.

Using the prevalence of active cases as a proxy for the number of pre- and asymptomatic, we get a preliminary indication for each country of whether either full opening, or blended opening with frequent testing, or no school opening at all, is advisable.

学习和教育是当前大流行中最大的两个世界性问题。不幸的是，在这项工作中看到，由于Covid-19潜伏期的延长，除非病毒在周边地区的传播得到完全控制，否则在2020年秋季全面开放学校似乎是不切实际的。 （例如，每百万人中有5个处于活动状态的案例不到）。

为了支持一些亲自学习的可能性，我们通过具有外部感染源和适当损失函数的SEAIR模型对每所学校内流行病的扩散进行建模，然后评估可持续的开放计划。事实证明，在课堂和远程授课的几天或几周内几乎定期轮换的混合模型通常是最佳的（接近）。在一个典型的例子中，最佳策略规定200天中有90天开放学校，与学校有关的个人中Covid-19案例的数量相对于无空缺增加了约67％，而不是约200％完全开放可能会增加。由于儿童的临床比例较低，

使用活跃病例的流行率来代表无症状和无症状的发病率，我们为每个国家提供了一个初步的迹象，表明是否建议完全开放或混合开放与频繁测试，或者完全不开放学校。