"Closing schools is the solution of reason", had defended the Minister of National Education, Jean-Michel Blanquer.
Since April 6, the classes have thus remained empty for three weeks in an attempt to bend the contaminations curve.
A measure that had been demanded both by part of the teaching world and by a majority of scientists.
But while kindergarten and elementary school students returned to school on Monday, the concern persists.
Have the school holidays made it possible to slow down the epidemic dynamic?
Attempted answer in three graphs.
A falling incidence rate
First observation: the incidence rate, ie the number of positive PCR tests per 100,000 people in those under 19, has undeniably fallen. Reading the figures from Public Health France, we see a peak reached on April 1, with 569 positive tests per 100,000 young people tested from 10 to 19 years old. The curve finally declined to reach 458 positive cases on April 12, before falling to 339 cases on the same sample on April 22.
The proof that the closing of schools has a direct effect on the transmission chains?
If "closing schools helps prevent contamination, it remains difficult to assess the effects of a precise measure", nuance Pascal Crépey, epidemiologist and researcher at the School of Advanced Studies in Public Health (EHSP).
"Is it the closure of schools that slowed down this rate or the fact that parents also sometimes took vacations to take care of their children and did not go to their workplace, thus avoiding other contaminations? ?
“Asks the specialist.
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Unsurprisingly, the latest peaks in the incidence rate correspond to the massive screening campaigns deployed in the establishments.
But here again, we must be careful when reading the results, insists Pascal Crépey.
“During a massive screening, you will search more and therefore inevitably find more cases.
The rate can climb, without always reflecting an epidemic dynamic in these age groups.
This is why the incidence rate is an indicator to be interpreted with caution, ”he notes.
Less frequent testing during school holidays
Be that as it may, the closure of schools has resulted in a considerable drop in the number of tests carried out. A drop in screening which had already been observed during previous school holidays. "Several factors may explain it: the closure of certain laboratories, the fact that people are no longer in the same routine and do not wish to be tested at their vacation spot, for example", adds Pascal Crépey.
Regarding the figures, there were more than 98,600 tests carried out on April 2 among 10-19 year olds, when classes were still open. A figure almost three times higher than that observed at the end of the month: less than 34,000 tests were carried out in this same population, on April 22. The incidence rate among adolescents is therefore falling, with the number of tests also declining.
Another observation: if the screening was almost divided by three during the holidays, the number of positive tests did not drop dramatically.
On April 2, there were more than 6,800 positive tests for more than 98,000 tests performed.
As of April 19, 4,620 positive tests were counted out of 37,000 screenings carried out in this population.
"The drop is there, but not in the proportions that one might expect", observes Pascal Crépey.
This is the finding that might surprise: the incidence rate among adolescents may drop, with a drop in the number of tests carried out, the positivity rate, or the percentage of people positive for Covid out of the number of people tested, him, only progresses.
Thus, more than 12% of the tests carried out on April 22 on 10-19 year olds were positive, against 9.5% on the general population.
Likewise, during the 15th week of April, (i.e. 12-18 of the month), the positivity rate among adolescents climbed to 12.5%, from 7%, the week of March 29 to April 4.
In other words, the students were tested much less during the holidays, but among those who were tested, there is a higher percentage of positives than usual.
A “stop of routine screening” during the holidays
How to explain such a finding?
“By stopping routine screening,” explains Fabienne El-Khoury, epidemiologist at Inserm.
“When you had a positive case in a class, you could imagine that all the students were going to get tested, even if not all were positive.
In this case, the positivity rate decreased mechanically, ”explains the researcher.
In other words, a "routine test" done during a mass screening campaign is less likely to be positive than when a person decides to go to a lab on their own with symptoms. .
"On vacation, the positivity rate has increased because the screening has been more targeted, which is not worrying", summarizes the researcher.
“For now, what we can say is that the drop in the incidence rate among the youngest is a reassuring indicator. It remains to be seen whether the figures will be just as encouraging in the coming weeks, with the reopening of classes… ”, she concludes.