Worldwide, countries closed their schools because of COVID-19. But in Switzerland, in three weeks from now, schools are supposed to reopen. Can this be done safely? Probably yes, but only with great prudence! It is not enough to hope that the kids will be fine. Instead, we need to design our measures in anticipation of occasional infections.

The virus is going to stay with us for a while. Schools must not start as if vacation was just over. Hopefully, those deciding about the format of re-opening will keep the scientific facts in mind when looking for (unconventional) approaches.

Fact 1: Children can catch the virus, and some can produce sufficient virus to pass it on to other children and their teachers.

First the good news: Children are rarely getting critically ill. About 90% of infected Chinese children were asymptomatic or had only mild to moderate symptoms. Sick children often have fever, dry cough, fatigue, congested or running nose; but also gastrointestinal symptoms such as nausea, vomiting, and diarrhea can occur.

Initially, the numbers of children reported to have COVID-19 were very small, but with increasing testing of non-severe cases, it becomes clear that a relevant proportion of cases are children. Even infants can catch the virus. Analyses of Korea’s massive testing show that children account for about five percent of the total cases. In comparison, children are about 18% of the Korean population. Does this suggest that children are less likely to catch the virus? Not necessarily. A systematic review points to current weaknesses in our understanding. It leaves it open whether children were under-sampled because they were often non-symptomatic, whether they were less infected because they have a smaller social network, or if they may be truly less susceptible. Still, Korea prolonged vacation to be on the safe side. Korean researchers recently concluded that closing schools helped reduce the spread and avoided hundreds of novel cases.

Very little is known so far about the virus levels produced by children. We have some data from case-studies. A  Korean neonate showed very high virus levels in the nasal liquid that are in the high-emitter range. In Singapore, there was a six month old baby carrying the virus for 16 days with high virus levels without any signs of the disease. A school child in France, on the other hand, had barely detectable virus levels. Actually, that child did not infect any of its peers in school. 

It would be dangerous to generalize from a few reported cases of low transmissions at school. Rather, we need to respect the evidence that children can get the virus and that some of them can show very high virus levels even without showing symptoms. If a child has high virus levels, it makes it very likely that a recipient of its droplets will get infected. Furthermore, in schools, we should not only worry about child-to-child but also child-to-teacher infections.

To address our lack of knowledge, we need carefully designed surveys of virus levels and antibody responses in children that were in contact with COVID-19 cases. These surveys also need to be including children without symptoms, ideally at multiple time points to understand more about the disease dynamics in these children.

Fact 2: Teaching indoors in class rooms will be challenging

In normal teaching style, teachers and children are often within „large droplet-distance“. This can be addressed by social distancing measures (if the room size allows) such as changing the teaching style to more frontal teaching, by seating children farther apart, or by building small plexiglass cubicles. Also frequent hand washing can be done in many class rooms.

However, the virus can be transmitted over longer distance also by small airborne droplets, though to a smaller extent. This becomes very important in indoor environments such as class rooms, where build-up of infectious concentrations can happen rapidly especially if a child is a „high-emitter“. While some classes can be held outdoors, often it will be necessary to stay indoors. Here, the only remaining option is to wear masks so that the virus cannot get airborne from non-symptomatic carriers. Fortunately, surgical face masks are highly efficient at catching the COVID-19 virus and also reusable cotton masks can prevent most emissions with similar efficacy if designed correctly.

Fact 3: Children are not small adults

Some of the measures known from the occupational health and safety field may work for children. We have little experience about the extent to which measures from the occupational health and safety field will work. We know that already apprentices face many challenges when dealing with hazardous airborne substances. Thus it is likely that such measures will be hard to adapt to Swiss schools. Still, it can make sense to apply the systematic occupational hygiene approach for identifying potential approaches along the S-T-O-P concept:

S= Substitution of “dangerous” close-contact teaching methods by other methods.

T= Technical solutions, such as additional tables, the above mentioned cubes, or individualised ventilations.

O = Organisational measures such as home-schooling for some of the topics, teaching in smaller groups, taking breaks inside the class room or training of correct hygiene measures.

P= Personal protective equipment (PPE) such as wearing masks (though they are mostly an emission protection, they do provide limited protection).

The occupational hygiene field has also a wide array of testing methods for examining the effectiveness of protective procedures. They range from transfer contamination studies using non-toxic fluorescent liquids and powders, to behavioural and usability studies that identify how and why workers (or school children) do or do not follow safety and health instructions.

Whatever measures will be taken, it will be crucial to test them thoroughly before they are implemented nation-wide. A feasible strategy could be to first investigate how well the measures work in a COVID-19-free community with volunteering COVID-19-negative students of different ages. Schools should restart only once tests with sham-contaminants and observational studies by usability experts confirm that the measures work.

What next?

It is clear that re-opening schools will be a major challenge. As long as there is no full containment of COVID-19, it will be inevitable that some infected children will go to school without knowing about their status. Some of these children will have a sufficiently large amount of virus in their air-lining liquid to be contagious. Thus, we must anticipate and prepare for this transmission risk by setting up pro-active anticipatory risk management. What does that mean?

Not every child should be allowed back to school: It will be important to allow only virus-free children back to school. For this to work, ideally a functioning contact tracing is existing that allows to identify all those children that have a risk of having the virus (even if it is small). This could be defined as being a contact of a contact of a case. All children that are in this „at risk“ group (or all children if no contact tracing exists) should remain in quarantine for another two weeks. Alternatively, if testing capacity allows, they could be asked as a condition to be admitted to school to participate in a daily sample pooling for a duration of two weeks. This approach pools samples from up to 10 individuals and tests them as a group. Only if a test is positive, all cases of the pool need to be assessed individually. This approach will allow daily testing for a „quarantine period“ with a limited drain on testing resources. Finally, children living with risk-patients should be exempt from going to school.

Start schooling in small closed social groups. In many school systems, children have more than one teacher and more than one group of peers. This can lead to a large number of possible contacts within the school. If one of these contacts is getting infected, all others will need to go into quarantine, which may mean that an entire school may need to close down. An answer to this are closed, non-overlapping social groups. I define this as a social groups of up to 10 children who meet with each other regularly in different constellations, from one to one to all together, as the teachers please (and by respecting hygiene rules). Non-overlapping means that they can be only in one social group such as a half-class and not attend activities such as school choir until the COVID-19 crisis is over. The key benefit of forming small groups is that we minimize the spread of the disease to too many people at once should one of the group members still get the virus. By asking for non-overlapping group, we minimize the risk that the virus can spread via the overlapping members, should one group get infected.

Schools must protect the teachers. Teachers spend all day long with the children. If one of them is infected, it is likely that the teacher will catch the disease unless the teacher is very well protected. Safety measures should be similar to those used by medical staff spending time in the same room as a patient.

Schools need a containment and testing strategy: It is almost certain that there will be COVID-19- cases in schools. Schools need to anticipate measures to be taken. It would seem appropriate to stop teaching the case’s closed social group, send them into quarantine and to admit them to a pooled testing effort. It could also make sense to start pooled testing of the wider circle at school, such as all other social groups that are occasionally in the same space as the case’s group, though they could be allowed to continue to go to school if a risk assessment suggests that they had a low transmission risk.

Transparent and open communication: It will be important to gain the trust of parents. For this, we need a very open and proactive communication strategy not only about what measures are taken but also about what and how information on potential cases is being shared. An ideal strategy could be to give weekly public dashboards on community levels and to inform the press and all parents „immediately“ about newly emerging cases in schools. It must be clear to the parents that they will be informed about cases in their class and school. Schools inform already today when one of the children has head lice. Thus, privacy concerns cannot be put forward as an excuse to not be open. Also the containment strategy needs to be communicated in clear and easy terms.


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Update on 29 April: Several links were broken and replaced by working ones.