What do we know about the role of schools in the Covid-19 epidemic? Five experts respond

The issue of school closures has been the subject of recurring debates since the start of the Covid-19 epidemic. It is now clear that severe forms of the disease only very exceptionally affect children.

But what about the ability of younger people to transmit the virus? Is keeping schools open problematic? Can their closure be effective? Why is it so difficult to achieve consensus on the question of the role of schools in the dynamics of the Covid-19 epidemic?

To understand this, we interviewed five experts.

"In our models, we do not consider that children have a different profile from adults"

• Mircea Sofonea, lecturer in epidemiology and evolution of infectious diseases at the University of Montpellier

Evaluating the contribution of children to the dynamics of the epidemic has been a crucial issue in our understanding of the epidemic from the start, but it comes up against major methodological difficulties and legitimately raises the question of the cost-benefit balance of measures targeting the school environment. On this subject precisely, all the conclusions of the studies have not gone in the same direction. Some French references initially minimized this impact, before the results of theComCor study by the Institut Pasteur, while the German and British references were more pessimistic. Germans say viral loads are also high in children than in the rest of the population, which has been confirmed more recently by American works. A British report had estimated that the transmissibility of young people (up to 16 years) is more than twice that of adults. Our neighbors across the Channel are all the more pessimistic as the variant that has emerged on their territory reproduces more easily in the youngest than the historical strain, what we have also seen in France.

One of the difficulties is to have data on these age groups and to be able to distinguish between over-contagiousness (risk of transmitting the infection) or over-susceptibility (risk of developing the infection at equal exposure). The youngest being mainly paucisymptomatic (show few symptoms) or asymptomatic, they do not meet the screening criteria (the French Pediatric Society has also limited the indications for PCR screening for children under six years old), which restricts the possibility of uncovering and extinguishing transmission chains passing through schools.

The questions of over-contagiousness or over-susceptibility of children have not yet been fully resolved.Sebastien Salom-Gomis / AFP

Another difficulty: it is complicated to determine the true contact rate of children and adolescents. But one thing is certain, by definition children have more contact than other age groups, because they are exposed to their peers. Should this overexposure be taken into account? Personally, I am in favor of having a rather parsimonious and conservative approach, in other words of not considering that children have a different profile from adults.

Unlike other teams like Vittoria Colizza's, we did not work specifically on schools. However, in our models, we do not make the children more or less contagious or more or less susceptible than the adults (on the other hand we do not integrate them in the same way in the models of hospitalization, obviously, since the severe forms do not. concern them only in a very exceptional way).

Regarding the implementation of restrictions, it is clear that the school is a place of contamination, whose closure represents an epidemic brake lever. But it is also too essential a place to be considered a primary target of restrictive measures.

"We tend to think that children will be less transmitters because they have asymptomatic forms"

• Pascal Crepey, epidemiologist and biostatistician at the École des Hautes Études en Santé Publique

What is clear is that it is complicated to follow the dynamics of the infection in schools, mainly because children do not have severe form, and few symptomatic forms. Unless you test them very regularly, whether they have symptoms or not, it's difficult to get a clear picture of the dynamics.

The question to be answered is "Do children have a greater contribution than adults in the dynamics of the epidemic". This is what would justify their being targeted as a priority by restrictive measures.

However, the dynamics of the flu teach us that people without symptoms, even if they do not isolate themselves, are less contaminating than sick people. Indeed, they do not cough, do not sneeze and therefore excrete less virus particles. Moreover, even if the studies diverge, their viral load is also lower, which means that they also have, a priori, less virus to shed.

From there, we tend to think that children will be less transmitters because they have asymptomatic forms. This is however compensated by the fact that the children will have a lot of contact with each other, and will surely respect less physical distancing, wearing masks, washing hands ... However, since the reopening of schools, protocols sanitary facilities have been set up. Even if their respect may vary from one school to another, they limit even more contamination in the school.

Children tend to have more contact than other age groups. Thomas Samson / AFP

Regarding the installation of the variant of British origin given that it is more transmissible than the historical strain at all ages, it can be expected that there will also be an increase in contaminations in the youngest, but it will be of the same order as in the rest of the population. The fraction of infections attributable to children will not change.

In recent weeks there has been a particularly important screening effort in schools. Between week 10 and week 11, the number of tests performed increased by 40%. This increase causes an increase in incidence since there are more positive tests. However, the incidence in 10-14 year olds remains lower than the incidence in adults. There are therefore infections in children, but they are more limited than in adult populations.

"The question of keeping schools open is above all a question of benefit-risk balance"

• Christele Gras-Le Guen, professor of pediatrics, president of the French pediatric society

A year later, the role played by schools in the dynamics of the epidemic remains one of the points on which communication is the most confused and the most difficult.

No one disputes that schools are a place of potential contamination and could harbor infectious hotbeds: we said that children were not very contagious, but we did not say that they were not at all. However, we note that in general, children tend to be infected by adults; the reverse is rarer. It is not impossible, but between what is possible in theory and what we see in practice, there is a difference. It is observed that contaminations occur mainly in the intrafamilial environment (meals and private meetings).

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One year later, what do we know about the infection of children with the SARS-CoV-2 coronavirus?

We have published an article which takes stock of the situation in France two months after the start of the September school year. We note not only that the viral circulation in children and adolescents is much lower than that observed in adults, but also that very few classes have been closed and that very few clusters have been investigated at the school. In addition, figures from the Ministry of Education indicate that very few teachers have been infected.

One point on which there is a lack of data is the question of the contagiousness of asymptomatic children, and their proportion. Indeed, so far the children who have been tested have been either because they had been in contact with a positive case, or because they were symptomatic, but no systematic test has been done on children. non-symptomatic. The arrival of saliva tests in schools has made it possible to better describe the carriage of the virus in the absence of symptoms in children. Thus, the National Education bulletin indicates that among 200 tests carried out between March 404 and 15, only 22% of students were positive and therefore potentially contaminating, which confirms that the contribution of asymptomatic children to the dynamics of the epidemic is marginal.

School is important for children's balance. The mental health of many of them has been affected by the health crisis.
Martin Office / AFP

This is not to say that the risk of epidemics at school does not exist. However, it is minor compared to the expected health benefit for children to leave schools open so that they can lead as normal a life as possible. It is all the more important that we see that the mental health of the youngest is particularly degraded by the health crisis. The question of keeping schools open is above all a question of benefit-risk balance which must be adapted to the level of circulation of the virus, to the age of the children and constitutes the last measure to be taken when all else has failed (strict confinement , optimized barrier measures, intensified vaccination of childcare professionals).

"Schools play a role in the dynamics of the epidemic"

• Dominique Costagliola, epidemiologist and biostatistician, deputy director of the Pierre Louis Institute of Epidemiology and Public Health

I fully understand that one can decide that it is important, for many reasons, that children continue to go to school.

However, a policy of saying 'keep schools open' involves putting in place measures that properly manage the risk associated with that decision (ventilation, masks, distancing, screening ...).

Keeping schools open means making sure that you have effective measures in place to limit the flow of the SARS-CoV-2 coronavirus to them. Denis Charlet / AFP

However, at the present time, given the very high circulation of the virus, I am not sure that this is possible. It is important to emphasize that the results published in the serious scientific literature have indeed highlighted than schools play a role in the dynamics of the epidemic.

On this subject, one point strongly calls out: how is it possible that we could have tolerated that the definition of a contact case at school is not the same as that used by Santé Publique France and the Caisse nationale d? 'Health Insurance everywhere else?

(Editor's note: in schools, if a teacher is positive, his students are not considered to be at-risk contacts "because the teacher wears a mask" - if only one child is positive in a class: the other children are not contacts at risk "because they are not very active in the chain of transmission of the virus." A class was closed only from three proven cases. Things have changed recently in the reconfigured departments: all classes will be closed "as soon as 'a first case will be detected'.)

This definition of the contact case made it possible to suggest that there was no problem in the schools. Abroad, in Germany and England, schools were closed when severe measures were taken. In a column published on February 24 in the newspaper Le Monde, Mélanie Heard and François Bourdillon clearly emphasized the importance of recognizing the role of school in the dynamics of the epidemic.

"If we want to keep schools open while further controlling the epidemic, we must ensure the effectiveness of the protocols"

• Vittoria Colizza, Inserm Research Director at the Pierre Louis Institute of Epidemiology and Public Health

The susceptibility of children and their role in the dynamics of the epidemic are points that were studied very early in the pandemic.

To date, the conclusions of this work have not changed: before the age of 20, people are less likely to be infected, and the contagiousness of young children is reduced.

There was probably an initial misunderstanding: some may have believed that children in school do not get the disease. This is not the case, as confirmed by the work of Arnaud Fontanet's team at the Institut Pasteur, on the risk of infection in pupils according to age. However, most cases went more unnoticed because they were asymptomatic. The cases were only detected when a symptomatic case arose, or after an investigation intended to trace the contact cases in an infected household, for example.

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Covid-19: schools and contaminations, what does science say?

The only novelty of recent months is that the British variant is transmitted more easily and is the cause of more severe forms, which - in conditions of high incidence like today in France - leads to detect more cases in schools now. In addition, under conditions the virus circulates less elsewhere since many places are closed, that people telework, inevitably, the contaminations in the schools take more importance.

One thing is certain, if we want to keep schools open while further controlling the epidemic, we must ensure the effectiveness of the protocols in place.

Saliva tests help increase participation, a key factor in screening correctly. Sebastien Bozon / AFP

Our latest work, carried out with Alain Barrat's team (CNRS), was precisely aimed at understanding whether regular screening in schools would reduce the number of cases. Based on contact data collected in a school of 250 students, we built a model of the spread of the epidemic within this establishment located in a “reconfigured” department. This model allowed us to compare the effectiveness of the protocol currently in place (class closure as soon as a case of Covid-19 is found in a child) with various screening scenarios (PCR on nasopharyngeal swab, PCR on saliva swab, antigen test on nasopharyngeal swab).

Closing the class according to the classic protocol makes it possible to reduce the number of cases within the school by 10 to 20% over a term. We compared this protocol with regular screening protocols: testing once every 2 weeks, once a week, twice a week, and every school day. We have found that the key parameter is not the sensitivity of the tests, but the frequency of screening, and adherence.
If only a quarter of the students participate (weak adherence, in the case of nasopharyngeal tests, unpleasant ...), it would be necessary to screen almost every day to identify cases and thus further reduce the spread of the epidemic. If three quarters of the students participate (case of saliva tests, less unpleasant), we are able to achieve the same levels of impact reduction on the epidemic by doing only one test per week.

If we want to keep schools as open as possible, we must therefore tend towards this type of protocol, which is much more efficient than the current protocol. Indeed, with the latter, the closing of the class usually occurs too late, it does not prevent the spread of the virus to other classes. In Switzerland, in some cantons, tests are carried out every week. In the UK, self-tests have been set up, twice a week.

Lionel cavicchioli, Head of the Health section, The Conversation

This article is republished from The Conversation under Creative Commons license. Read theoriginal article.

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