June 30, 2022

current screening in primary school does not break the chains of transmission

This is not very encouraging news, coupled with a way out of the deadlock. The SARS-CoV-2 screening strategy, as it is deployed today in all elementary schools in France, does not seem able to break the chains of transmission. With this protocol, “The number of children detected positive remains insufficient”, explains Vittoria Colizza (Inserm, Sorbonne University, Paris). This is one of the conclusions of the modeling that she coordinated, published Thursday, December 9 in pre-print.

Since December 6, as soon as a student is detected positive, each student in the class must be tested; then, only children who are positive or who refuse the test are required to stay at home, with the class only closing in the third case. The purpose of this so-called “reactive” protocol is to limit class closures that are harmful to students.

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“Another method of screening would make it possible to stop the circulation of the virus within primary schools, thus protecting children and those around them against infections”, emphasizes Vittoria Colizza. This is the so-called “iterative” protocol. Clearly, a test is offered every week to all children in the class, without waiting for one of them to have been detected positive. Only contaminated schoolchildren are then sent home. The advantage of this protocol: in children under 10, asymptomatic cases are very frequent, justifying repeating the tests in the greatest number. A crucial issue, as the incidence rate of infection soars in 6-10 year olds: on December 5, it was 988 cases per 100,000 inhabitants, against 666 cases a week earlier and 347 two weeks previously.

How did the authors proceed? To develop their model of the circulation of the virus at school, they relied on data collected in France, before the pandemic, in a primary school and a secondary school.

Groups of children and teachers were fitted with radio frequency chips measuring their proximity contacts during their various activities (lessons, recreation, sports, canteen, etc.). Based on these data and the results of pilot screening carried out in 683 schools during the Alpha wave in spring 2021, the researchers developed a first model. A model that they then corrected by the incidence of the epidemic in the rest of the population, to take into account infections introduced at school, and by the prevalence measured in schools.

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