One group on site, the other at home teleworking: the best strategy to prevent a case of Covid from leading to an epidemic outbreak in a company, a school or a high school is to organize work in half-groups , with a rotation system.

This is indicated by a study carried out by several research organizations including the CNRS, INRIA and the University of Paris.

The authors sought to find out which measure was most effective in "stopping an epidemic spread in a community from a first positive case".

Four different strategies studied

For the three places studied (a company, a primary school and a preparatory class in a high school), the result is the same: "from best to worst: a weekly rotation, a daily rotation, a weekly alternation and a daily alternation", concludes the study, published in the journal

Plos Computational Biology

.

The work-study strategy, which may be preferred to maintain cohesion between employees and students, consists of everyone going to the office or to class at the same time, then staying at home at the same time.

The rotation divides the group in two: a group A going there while the group B stays at home, before reversing.

This “hybrid” system was set up in part of French colleges and high schools during the previous school year and could make a comeback if the health situation deteriorates, even if for the time being, the start of the school year is “face-to-face”. for all students.

Weekly rotation, the most efficient system

In detail for the case of primary school, in the absence of any measure, the researchers estimate that there is more than one risk in four (27.3%) that a positive case leads to an outbreak. epidemic (defined as at least five other infected people). This proportion drops to 17.3% with a daily alternation, 16.6% with a weekly alternation, 12.3% with a weekly rotation and 12% with a weekly rotation. The latter device is also the most effective for extending the time before the first case leads to an epidemic focus and for reducing the total number of infected people.

However, these strategies only work if the circulation of the virus is still limited.


Thus, in the case of high school, if the local reproduction rate of the virus before taking measures is greater than 1.7 (that is to say that each infected person in the area concerned contaminates an average of 1.7 ), "None of these strategies, apart from full-time distancing, is sufficient to prevent the emergence of an epidemic focus".


On the other hand, with a reproduction rate between 1 and 1.38, the four strategies make it possible to bring it back below 1, the bar which marks the limit between a growth and a regression of the epidemic.

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