What the Numbers Say: Delta and the Classroom
On Friday, September 10, Fields hosted a panel discussion geared toward parents, students, teachers, school administrators and staff. The intent was to address fears, anxieties and concerns over the return to the classroom, particularly in light of the highly transmissible Delta variant, and to provide tips on how to minimize the risk of infection.
Prof. Lydia Bourouiba (MIT), an airflow expert, Dr. Nisha Thampi (University of Ottawa), a pediatric infectious disease specialist, and Dr. Ashleigh Tuite (University of Toronto), an epidemiologist and mathematical modeller, answered questions submitted by the audience. The transcript highlights below have been edited for length and clarity.
Q: We have two cohorts that are at school right now: the 12-and-over group, a majority of whom are vaccinated, and the under 12s who are not. What are your concerns for these two separate groups?
Dr. Ashleigh Tuite: In a sense, I would say it's a little bit more complicated for the over-12s than the under-12s, which may seem counterintuitive, but we know that if we don't have protections in place in the under-12 population – spending time indoors, breathing shared air, particularly at a period of time where we have the Delta variant – we know the majority of children will get infected in the absence of any mitigations.
Thankfully, most of those children who get infected will be fine, but some of them will have severe outcomes. We're starting to see that unfortunately play out in the United States right now, where we're having really high infection rates in kids. And we're starting to hear stories of hospitals being overwhelmed or having record numbers of children hospitalized with COVID.
The other piece that we talk less about are the longer-term consequences of COVID infection, long COVID, which is something we're still learning about. But I know most parents would want to avoid having to learn what the longer-term consequences of a COVID infection mean, and we do that by protecting our children. The more complicated question for the 12-and-overs, those who have had a chance to be vaccinated, relates to the fact that we have high levels of vaccination in that age group but it's not high enough to completely shut down transmission. We need to have much higher [vaccination] levels than that to really shut it down.
So, in that cohort there may be this sense of, and I think that's also reflective of the adult population, which is, "We've been vaccinated, why can't we get back to the life as normal?” And the reality is that we still need to have these other protections in place. People who are vaccinated are very well protected against severe illness but they can still get infected. The thing we talk a lot about is the fact that our communities are connected to our schools and that works both ways. So, what's happening in our communities reflects what we'll see in our schools [and vice versa]. And we know that the virus is going to find the vulnerable, whether they be unvaccinated or immunocompromised.
At this point I think the greatest risk is in children. Last spring when the vaccines became widely available, there really was this hope and optimism that we would return to school in September with some degree of normalcy. The reality is that, in a sense, we're in a far more precarious situation this year than we were last September given Delta and given the fatigue that societally we feel and this desire to really just be done with the pandemic.
Q: Can you talk about your concerns for the under-12 group, specifically?
AT: For the under 12s the biggest concern is that if we don't protect them, the majority of children will get infected. Delta is just that transmissible. So, what that means is that we really do need to continue to have these layered protections in place in order to really ensure that this isn't forever. We have a vaccine that is being trialed in children right now and I think in the next month or two it’s likely to be approved for use in children. Once children are able to be vaccinated, that really shifts the conversation, and we get closer to a point where we can be talking more about what our pandemic endgame looks like. For now, though, in terms of what it means for children, there are the direct COVID implications in terms of illness.
But we've had a year and a half of disrupted education and there's been a lot of talk about how we can't shut down the schools again. And the reality is that if we don't have these protections in place, both within schools as well as a broader community response, we are potentially facing more disruptions in education, whether it be individual class dismissals or children having to be isolated and quarantining because they've been exposed in school. So, it really is a matter of not only protecting them from COVID, but also protecting them from increased educational disruption.
Q: What is the progress on a vaccine for the under-12 cohort?
AT: It's an excellent and very timely question because there was just some information released in the news today [September 10] saying the Pfizer vaccine is expected to release some information on their trial results in the five-to-11-year-olds in the coming weeks. The Pfizer trial is wrapping up and so they're going to share that information with the regulatory authorities. We would expect to see the pharma companies starting to seek approval for the vaccine as early as October. We're not there, but we're getting there. I think it hasn't happened as quickly as we would necessarily want, but they've had to go through the process testing these in the under-12 age group, making sure that they're safe and effective. But I think come late fall, early winter, the expectation is that we will have vaccines for the under 12s.
Q: How much greater is the risk of hospitalization for those who are under 12 versus serious illness from other things like the flu?
Dr. Nisha Thampi: It's a good question, but it's actually hard to answer because we haven't yet seen levels of flu circulating like we're seeing with COVID-19. It’s hard to say at this point whether the risk of hospitalization is greater because we also didn't do such broad testing in the community for RSV or influenza in the pre-pandemic period to be able to say out of all the kids who are getting infected, what's the proportion who are getting admitted to the hospital? But I don't think it's that uncommon for kids to require hospitalization or to be hospitalized and have COVID found in their admission test.
Then there's a question of whether it's relevant to even talk about kids who are being admitted for one thing and happen to be COVID-positive versus admitted because of complications related to COVID-19. I'd say from a systems level that's really important because we use the same protective measures in kids who happen to have COVID-19 and kids who are admitted with COVID-19. The pressure on the hospital system to have the appropriate precautions in place and the appropriate workflows for them is the same, regardless of whether it's a bystander-type of infection or the reason for their admission.
Q: What do COVID symptoms look like in kids versus adults?
NT: Where we have to start is that approximately one-third [of infected children] will have no symptoms at all. So, in that proportion of kids who do have symptoms, the most common can be very minor: 60% can present with a runny nose or sore throat or a dry cough, which I think most parents can relate to as not a reason to keep them home to school or avoid a play date or a family gathering. But in the present period, where we have a mix of individuals who are fully protected from severe disease and who may have been fully protected but have waning immunity, it's really important for us to think about these minor symptoms as a red light, whether it's going to school or connecting with family or friends or doing extracurricular activities even though there is an urge to get back to all of those activities.
And when we have so many adults around us who are vaccinated, these are also the most common symptoms for them if they were to have a breakthrough infection. So again, it speaks to the importance of being mindful of some of your own symptoms and the symptoms of members in your household and getting tested, especially if you do interact with vulnerable or vaccine-ineligible individuals.
Q: You're talking about asymptomatic kids and some other symptoms that are subtle. When should you get a kid tested?
NT: If a child has a runny nose or a sore throat, then they don't go to school. And that is a habit I hope we'll keep for the post-pandemic period. They stay at home and they self-isolate. And if they're still unwell or they have developed more symptoms, including fever and a cough, then they go in for testing. If their symptoms are improving, then it's recommended for them to go back to school. So, that that can make some families uncomfortable if they never had that system in place. But I have to say, it worked really well last year in Ottawa in terms of still having low rates of transmission in schools and that's likely because we had a fairly consistent application of health and safety measures in schools as well.
Q: The Toronto Star reported that there's a new variant called Mu that’s been detected in Ontario. How concerned should we be about this?
AT: We keep hearing about these variants and we're going to keep hearing about these variants. The reality is that we're effectively watching the virus evolve and adapt to living in humans in real time, which is not something that most of us, myself included, have done before.
What we're seeing with Mu is that… at this point, it certainly doesn't seem to be more transmissible than Delta. So that's reassuring in the sense that it's unlikely to out-compete Delta. One of the reasons that people are watching it and are concerned is because it does appear to be potentially immune evasive. Obviously, we don't want to ignore it as we wouldn't want to ignore any other variants that occur, but it's really challenging to predict where exactly things are going to head.
Q: Professor Bourouiba, your research has appeared in media and it includes these amazing 3D models that show how the virus can be transmitted in a classroom. You looked at masking versus unmasking, airflow and transmission within classrooms. Talk to us about what your mathematical models found.
Prof. Lydia Bourouiba: Thank you. As a disclaimer, this was based on a synthesis of part of my work that combines modelling and experiments, but also the work of many others over the past year and a half now. What is really important to understand is that there is no single magic bullet to really tackle what we are going through right now, as we have seen after the introduction of the vaccine. We are in a fourth wave despite the fact that a vaccine has been found in record time compared to the regular history of vaccine research and deployment. On the other hand, we are really faced with a fight against evolution, with a virus that is adapting, and that is why we have this additional wave.
In classrooms, we are talking about a number of children who might not have access to the vaccine yet [and who are] sitting in enclosed spaces for a long time – at least an hour, maybe even a bit more, but with some breaks – and we are talking about children who might not have access to or even the knowledge of how to use protections like masks that are tight-fitting and that would, in fact, be filtering the air they inhale and exhale.
[All] this is what adds to the complexity of the topic, and the insights, therefore, have to really combine various strategies – the strategy of managing the airflow, the strategy of managing how to place individuals with respect to that airflow, the strategy of separating by distance and also time of exposure, and the strategy of trying to also leverage at a more generalized scale how to maybe even occupy that space at all. If we can't have everybody using that space at full density, how do we stagger the usage of space in terms of bubbles or pods and manage both the air cleaning and the surface cleaning between the usages? I can expand further in a lot more details, but that's in a nutshell what the document and the work that we have been doing is about.
Q: One of the things that I found really interesting [in your research] is this concept of ‘hot zones’ in a classroom and they can be around entrances and exits. Can you get into how much they matter, and how teachers and administrators maybe need to think about those areas in classrooms?
LB: In terms of hot zones, particularly around inlets and outlets [i.e., entry and exit points in a room], we recommend an increase in the portion of clean air injected at high rates to compensate for the ventilation indoors that might not be to the standard we would wish to have for infection control. For that, we have different strategies.
- Use natural ventilation. Essentially, opening windows or doors to create currents that will locally inject more airflow and directional flows and locally expose the contaminated air from another outlet.
- Compliment the airflow injection by having airflow creation through localized devices, like a HEPA air filter, that you would add on to the building venting already in place. That, too, creates localized flow patterns that can be relatively strong depending on the strength of the airflow setting and the device being used.
Simple principles people should keep in mind when doing this: Because you would be injecting fresh airflow, or essentially removing contaminated airflow from a localized zone that is at the height of the occupants (if you're talking about a window or an air filter on the floor or on table), you’re creating potential directionally strong airflows toward that entry point or exit point. This creates concentration areas where a big portion, prior to that intervention, could essentially be directed. So, without any interventions, an individual sitting too close to such an exit point would cumulatively over time be exposed to more viral particles than average from the other occupants.
It's very important to have these interventions in place to lower the average. But because we don't have homogeneous mixing and we potentially have disturbance of the airflow patterns by adding these points of fresh air input or output, we need to ensure that we do not place the air cleaners too close (rule of thumb: one-to-two meters away) to that exit point.
For the entry points, of course, there could be benefit for the individual to be exposed to the very clean, fresh air that's coming from outside or a device. The issue is if one of those individuals becomes infected [with COVID], even if they’re asymptomatic, we would have a very concentrated plume [of infected airflow] that would be extended from that individual because of the strong directional airflow that’s coming out of that point. So, we shouldn't have anyone sitting too close to the entry or exit points.
Q: For teachers and school administrators who are watching, what are some practical tips for setting up a classroom to minimize the potential for spread?
LB: The air we breathe is really the medium from which this virus is infecting us. It’s an inhalation process that needs to occur. So, as much as surface cleaning and management of common surfaces remains important, particularly with kids that might be putting their hands everywhere and not wearing masks, the airflow is [key]. We have the tools. Just keep in mind how to position individuals in the room, that the buildup in a room [with a lack of] the right filtration is really what would lead to high exposure over time, particularly lunchtime. Have kids that are unmasked outdoors as much as possible. If you could do everything outdoors, in fact, do that, including teaching. I'm sure it could be a great experience for kids (weather permitting).
The tightness of the mask is as important, if not more important, than the [air] filtration level itself. If you have a high filter but you have gaps in the side [of masks], fluids are lazy and flow is going to go through the path of least resistance wherever it's open. For kids, there are adapted masks that can be tight-fitted. It’s very hard to say if they would be able to keep them on for that long, so that's why outside versus inside [is better]. If they are inside, make sure the air is filtered or cleaned or refreshed as frequently as possible.
But the last point I want to just highlight very quickly is distance. There was a lot of debate about these distances. It's not the big blobs of drops that matter, it's the airflow. When you're close within the two-meter distance [of someone else], what you can have with unmasked kids is exposure to a highly concentrated cloud that is still not yet spread out and diluted in that space. That airflow needs time to dilute or needs an obstacle. That's what we're trying to achieve with all these measures. I think understanding these principles hopefully helps [administrators and teachers] make all these decisions.
For more tips on how to set up and manage safer classroom spaces, have a look at Prof. Bourouiba’s Healthy Teaching guidelines.
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