Making it safe to go back to school in this COVID-19 pandemic

Every parent will tell you that kids get sick when they go back to school, which they then generously pass on to parents. Returning to school after the summer vacation will be no exception, except this time the COVID-19 stakes are far higher.

Each region struggles with how to make their schools safe and propose rules that are many and varied. My three kids go back to school with new rules that are different implementations of masks, smaller classes, distancing, etc. I have my doubts that they will work simply because kids and teachers are human, and there will be lapses and mistakes, even deliberate breaking of rules -the same teenagers who have such a great need to socialise and have been having clandestine gatherings during the vacation will be flouting the rules when out of sight, and meeting each other after-school.

Last week I got on an airplane from Belgium, where I live, to Greece. I had to present a certificate for a negative COVID-19 PCR test before I was allowed to check in, and that was very comforting indeed. Kudos to the Greek government for imposing such a rule. On the way back there is no such rule and I am more concerned as a result. That got me thinking …

Return to school can be considered a risk but could also be an opportunity if we could test every child and teacher as school begins. If we have a snapshot of the individual infectious state of all children at that moment in time, our schools would be so much safer for a bit, any lapses in rules would be less concerning, and we’d have better data to work with.

Testing all children and teachers at once is a logistical challenge, no doubt, but also aided by the fact that we have them all in the same place at the same time. Wouldn’t it be great if – say – we could test all teachers a day or two before school starts, and all children in the first week of school when the rules will be most studiously enforced and respected?

The problem is one of logistics. Take Belgium as an example:

There are roughly 2.3 million children attending education in Belgium. 400,000 are in pre-school, 800,000 in primary school, 800,000 in secondary school, and 300,000 in higher education. Assuming an average class size of 23 (I’m just talking rough numbers here) gives us 100,000 teachers.

Belgium can run, as far as I can check, about 25,000 PCR tests a day. Clearly testing every child would take too long. However, samples can be pooled. That means that one can take a number of throat swabs, stick them in a blender, and do a single test on the mix. A study published in April in the Lancet[1] shows that a pool of 30 is achievable – the threshold cycle value[2] is a bit longer, but quite reasonable:

So, assuming one would give priority to teachers, we could get them into school the week before term starts (teachers are usually at school then to make preparations) and throat swab them all by the local doctor (it doesn’t hurt, I’ve had it done twice). Put the samples in pots of 30, note the names, hopefully in an electronic database (in Belgium, we all have electronic ID cards which makes that easy) and send them off to the labs. That would be a total of 100,000 / 30 = 3,000 PCR tests – or about 10% of Belgium’s capacity, so the results are back within a day.

We’ve had about 3,500 new cases in Belgium in the last seven days in Belgium for a population of 11.5 million, or about 1 in 3,000. The probability of at least one of a random sample of 30 people being infected is then:

=1 – (1-1/3000)^30 = 1% or thereabouts.

So 1% of tests (around 30) would come back positive, and everyone from those pools (around 1,000) could be tested individually the following day. Before the end of the week, we’d be pretty sure that the teaching population was COVID-free with just 4,000 tests.

Then we test the kids. Best would be to test in natural cohorts, i.e. by class. Assuming the 23 children per class, we’d need 100,000 tests. We could get that done in the first week of school, with 20% testing capacity left over for emergencies. We could impose really strict rules for that week, and individually retest the children in those groups that came back positive. By Tuesday of the second week we’d pretty much eliminate COVID-19 from the schools – for a while at least.

If we also urged parents to really make sure that their kids were quarantined for that one weekend after the first week of school, we’d be even more sure our schools are safe. We’d eliminate schools and colleges as a driving factor for the infectious spread. We’d also have excellent data for contact tracing.

And if every country that was able to did the same, since most schools have tight catchment areas, we’d have the most consistent comparable data for establishing the true infection levels in high geospatial resolution.

Does that make sense, or did I miss something?

My thanks to Arianna Mussida for pushing me to think about this.

[1] “Pooling of samples for testing for SARS-COV-2 in asymptomatic people”. The Lancet Apr 28, 2020. DOI: https://doi.org/10.1016/S1473-3099(20)30362-5

[2] A threshold cycle value is the number of amplification cycles needed to ensure that an infected sample will generate enough amplicon product above background to be sure of a positive test result.