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ScienceMay 2, 2022

Siouxsie Wiles & Jin Russell: What we know now about Covid and schools

black and white photo of a classroom
Getty Images/Tina Tiller

As kids return to school for the first time under orange – in many cases, without masks – microbiologist Siouxsie Wiles and paediatrician Jin Russell share the latest research on staying safe in the classroom.

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School students in Aotearoa New Zealand are heading back to class today. Covid-19 cases are still in the thousands per day, but the country being at orange which means masks are no longer mandatory in educational settings. We’ve made no secret of the fact we think masks should stay, and we’ve been contacted by lots of worried parents and teachers. So, to help everyone understand what to expect in the coming weeks and months, we thought it might be useful for us to explain what the evidence is saying about Covid-19 and schools.

The US Centers for Disease Control (CDC) website has a regularly updated summary of scientific studies of Covid-19 transmission in schools. This Evidence Brief identifies four major factors that impact the amount of Covid-19 in schools. We’re going to go through these four factors below to explain why Covid-19 in schools is more dynamic and variable than most news headlines suggest.

First though, we want to be really clear: schools and ECE are essential services for children and their whānau. Alongside formal education, they are settings for friendships, connection, a sense of belonging, books and resources, sports, kapa haka, free school lunches, and much more. Some young people thrive with remote learning, but many others struggle. Overseas data shows that students from disadvantaged homes can fall behind when schools are closed and struggle to catch up again, harming their long term prospects. Schools are the places where students with learning difficulties can receive extra educational support, and where some students with disabilities see their therapists. Importantly, schools form part of the social security net, with counsellors, nurses, social workers, and safe adults, to support children and young people who face challenging circumstances at home.

That’s why we think it’s important that schools stay open as much as possible during the pandemic. And because there are teachers, children, and families in our community who are more medically at risk from Covid-19, schools need to be safe and inclusive for everyone.

The classroom is just one place that kids congregate while at school. (Photo: Getty)

Germ factories or safe as houses?

There are lots of false and unhelpful narratives about Covid-19 in schools. Ironically, the two main ones are at opposite extremes to each other. On the one side is the narrative that schools are super-spreading environments. On the other is the narrative that schools are safe, low risk environments no matter what. The reality is that schools are much more variable settings than either of these narratives suggest.

While some schools have clearly done very well through the pandemic and seen little transmission, there are lots of families who have been able to shield almost completely except for attending school, and who can pinpoint that the virus came into their homes from school. But one of the difficulties of understanding Covid-19 in schools is being able to tease apart what transmission is happening in classrooms versus during school-related or adjacent activities like drop-offs and pick-ups, after-school activities, birthday parties, and school camps.

Another complication is the way New Zealand schools are run. Every state and state-integrated school and kura in the country is governed and managed by an elected board. The board sets the strategic direction of the school and is responsible for health and safety as well as employing the school’s staff. While the Ministry of Education sets the rules and guidelines, it’s up to each individual board to decide how those rules and guidelines are implemented.

It’s easy to see then how a school with a board that’s been following the science of how the virus transmits and is able to put in place robust protocols to minimise transmission can have a very different experience to a school whose board is strongly influenced by members who don’t believe in Covid-19, or who think that the best approach to dealing with the pandemic is to just let everyone get infected so we can “get back to normal”.

Each school community is unique as well, with differing levels of vaccine coverage and spread, and this ends up mattering a lot too, as we will now explain.

The four factors that impact Covid-19 within schools

Factor one: Community incidence

The first factor that impacts the level of Covid-19 within schools is how much Covid-19 there is in the local community. This is intuitive. When there are many infections in the community, more infected students and staff may come to school. When there are fewer cases in the community, fewer infected people will be at school. The point is this: transmission in schools is dynamic. It varies based on the context. This is where we need to dispel the first unhelpful narrative that schools are super-spreader environments.

Many people think that schools must be super-spreaders settings because so many school-aged children have caught Covid-19. At the time we wrote this, young people under the age of 20 made up almost one third of all active cases of Covid-19 in the country. But remember that young people under the age of 20 also made up one third of all active cases in October 2021 during the Auckland delta outbreak when schools had been closed for weeks. At that time, Covid-19 spread was predominantly happening in households – children were catching Covid-19 at home.

Many will have seen news headlines reporting the numbers of Covid-19 cases connected to schools and daycares, often in the thousands or tens of thousands per week. These headlines also feed into the narrative that schools are super-spreaders environments. But these numbers don’t actually tell us how much Covid-19 spread is happening within schools. The numbers are reported by the Ministry of Education, but are based upon reports from school principals, who in turn get told about Covid-19 infections by school parents and caregivers.

Omicron is so transmissible that tracing every infection back to its source is no longer possible. So to understand how much transmission of Covid-19 actually happens within schools, and why we are confident that our schools are not super-spreading environments, we need to delve into the evidence base from overseas studies. What’s remarkable about these studies is that they consistently show that schools can be surprisingly good at stopping chains of onward transmission of Covid-19 when certain preventative measures are in place.

For instance, a huge study of over one million students and staff in Wisconsin and North Carolina published earlier this year found low rates of within-school transmission even when schools returned to full in-person learning over March to June 2021. In this study, for every 20 community-acquired infections, there was one within-school transmission event. At that time, mask-wearing was universal in schools. This finding is in line with many other published studies. 

But what about delta and omicron? Omicron is highly transmissible, so how can we be confident that schools aren’t super-spreader settings with omicron?

Epidemiologists at the National Centre for Immunisation Research and Surveillance (NCIRS) in Australia have been carefully tracking Covid-19 transmission in schools in New South Wales throughout the pandemic. In their latest study, the proportion of close contacts who tested positive for Covid-19 after exposure at school, also known as the “secondary attack rate”, was 2.4% for delta, and 3.7% for omicron. This means that for every one infected student or staff member who came to school with omicron, 3.7% of their close contacts went on to test positive for Covid-19 due to transmission at school.

The NCIRS school studies are useful for Aotearoa New Zealand because we have similar vaccination rates and Covid-19 strategies in schools to New South Wales. The NCIRS studies are also very reliable, because close contacts are followed up with PCR testing regardless of whether people had symptoms or not. This is important for accuracy because children often don’t have symptoms so can go undetected.

It’s clear that the risk of spread within classrooms can be kept low compared to other settings – for instance, secondary attack rates in households in the same NCIRS study were over 60%. This is why you may have heard schools being described as “lower risk settings”.

While the risk of onward transmission can be kept lower compared to other settings, it is clearly not zero risk. This brings us back to the idea that the level of Covid-19 in the local community matters. We need to dispel the second false narrative, that schools are low risk environments no matter what. If there is a lot of Covid-19 in the community, there is a greater risk of spread within schools. Each infected person coming to school poses a small but cumulative risk of onward spread to others.

The good news, however, is that when the right strategies are in place, schools can do remarkably well at stopping most chains of transmission. Let’s look more closely at these strategies now.

Focusing on good ventilation while inside is key (Image: Getty Images/Tina Tiller)

Factor two: Taking a multilayered approach to preventing Covid-19

Jin has previously written about strategies to prevent Covid-19 transmission in schools, also called the “multi-layered approach” here and here. Improving ventilation in classrooms, using portable HEPA air cleaners where needed, universal mask wearing, good hygiene, and cohorting students into groups to prevent a lot of mixing are all part of the toolkit. Lots of testing in the community also helps. Every person who stays home when they have Covid-19 snuffs out a potential chain of transmission. When community case numbers are high, the more layers of protection, the better.

Clean, fresh air is a key layer of the strategy. Focusing on better ventilation is smart – it reduces the risk of spread for not only Covid-19, but other viruses as well, and protects everyone in a space without any inconvenience. The Ministry of Education has developed guidance for schools to improve ventilation in conjunction with indoor air quality experts. We’ve lots more to say about this, but will save that for another time. What’s important is that if we can improve ventilation in schools, we’re likely to see tremendous gains for child health which will last beyond the pandemic.

That data is really clear that Covid-19 can cause outbreaks in schools when prevention measures aren’t in place and particularly if there is high transmission in the local community. Like this study, which tracked a Covid-19 outbreak in a primary school in Geneva. However, outbreaks don’t tend to occur when the multi-layered approach is in place. This is why, with winter approaching we think masking should remain a key pillar of our response at orange. It makes no sense to us to remove them, frankly.

There’s one more important thing to mention before we move on. We need to think about school-based activities, not just classrooms. That big study in Wisconsin and North Carolina we mentioned earlier found that almost half of all the secondary transmission events within schools were linked to sports activities. The researchers were not clear whether it was the sports events themselves, or social gatherings between sports players, that led to the spread. The NCIRS report also found that when school outbreaks did occur, they tended to be linked to out-of-school activities and gatherings, such as sleepovers, parties, ride-sharing, and indoor sports. Clearly, we are not saying that children shouldn’t play sports. What we’re saying is that focusing all our attention on classrooms will miss a key point: spread happens wherever prevention strategies aren’t in place. Simply closing schools to try to curb community transmission doesn’t solve the problem.

Factor three: Immunity from vaccination and infection

The third factor that affects Covid-19 in schools is how much immunity is in the school community – from vaccination and from infection. We would much rather that people got their immunity from being vaccinated, rather than from infection!

While it is true that being vaccinated doesn’t guarantee that a person won’t catch omicron, being triple vaccinated can reduce transmission. At the moment, just over 70% of people who are eligible are boosted, and younger and middle-aged adults have lower levels of booster coverage than older adults. If all the parents and adults connected to schools who are eligible got boosted, this would protect them from Covid-19 and help reduce transmission in the community, and by extension, in schools. Sixteen and 17 year olds are also eligible to be boosted six months after their second dose so we encourage them to take that up.

Photo: Getty Images, additional design by Archi Banal

For children, being vaccinated is primarily about protection from serious illness if they did catch Covid-19. While 93% of 12 to 17 year olds have had two doses of Pfizer, only 55% of 5 to 11 year olds have had their first dose, and 23% have had two doses. Most of the primary school children who have been vaccinated got their doses in the first three weeks of the vaccine rollout before schools reopened. But many parents hung back. What’s important for any parent who is sitting on the fence to know is that the Pfizer vaccine is very safe for children.

Even if your child has already had Covid-19, it’s still a great idea to complete the full course of vaccinations – wait for three months after they’ve recovered and then get the remaining doses. This leads to hybrid immunity, a broad, strong immunity that sets your child’s immune system up well for the long-term. Because omicron won’t be the last variant.

Factor four: The circulating variant(s)

The final important factor is the Covid-19 variant(s) circulating in the community – what are the symptoms, how well does it transmit, and how well do the different public health measures work to reduce transmission? The virus is evolving. While delta was different to previous versions of the virus, the vaccines were really effective at stopping people getting infected in the first place.

Omicron is different to delta and while vaccines are still preventing serious illness, they aren’t doing as good a job at preventing transmission. But how might the virus be evolving right now? And what might the next variant be like? Siouxsie’s written before about her concerns at people calling omicron “mild”. It isn’t. We’ve just got better at preventing and treating Covid, at least in the short term. But it’s still deadly. And that doesn’t factor in the potential long term consequences of infection. People also need to understand that it’s not “one and done”. There are people who are now who have had Covid multiple times.

At the moment, the dominant variant here is BA.2. But there are other omicron variants around. We’ve just had our first report of XE, a recombinant which has a combination of genes from the BA.1 and BA.2 variants. South African scientists have recently reported that they’ve identified two new omicron variants, BA.4 – our first case of which was identified at the border yesterday – and BA.5. Early data suggests they may both be more infectious than BA.2.

Remember though that omicron came out of nowhere. At the time BA.1, BA.2, and BA.3 emerged, we were facing the delta variant and wondering how it might evolve. What we’ve learnt from omicron is that a completely different variant may well explode on the scene at any point. And the more transmission there is, the more chance of new variants and recombinants (versions of the virus that are a combination of different variants) evolving.

Globally there is a lot of transmission happening. Much of it is being driven by the fact that many countries have moved to the “we need to get back to normal” phase of the pandemic and are ditching most if not all public health measures, including testing and genome sequencing. This means we likely won’t even know the next new variant has emerged unless or until there are cases in a country that is still testing widely and/or routinely doing genome sequencing, like South Africa.

So what should we expect to happen in schools in the weeks and months ahead?

We’ve laid out the four factors that impact Covid-19 in schools, and shown that the evidence is really clear that schools can be kept open safely even when cases of Covid are high in the community. What is required to achieve this is a commitment to having strong layers of protection in place, especially if and when case numbers start to rise again.

The coming winter could be tough. Immunity from vaccines and infection is now waning. The colder weather means we’ll be spending more time indoors, and are less likely to have doors and windows open to improve ventilation. Masks have been removed from lots of environments and more mixing is allowed under orange. The border is reopening and MIQ largely removed which means any new variants evolving overseas will arrive here too, on top of influenza and other viruses like measles that we haven’t seen for a while. Of course, we could also be evolving our own new variant too.

All these together means that the community incidence of Covid is likely to increase, if it isn’t already, and this will impact schools.

Some schools are ahead of the game, and are keeping masks just a bit longer, through winter. It’s easier, after all, to keep a good habit in place, than to take it away and have to put it back. If you haven’t already, ask your school what prevention strategies they are keeping in place and what their ventilation strategy is. Encourage your children to wear a good-quality mask when indoors. And if you haven’t yet taken up the opportunity to be boosted or for your children to be vaccinated, please do that too.

In the first 18 months of the pandemic, Aotearoa New Zealand topped the OECD for the number of days schools were fully open. While students were shut out of school for long periods overseas, our young people were reaping the benefits of our bold, collective action. We know what protections make for better outcomes for everyone. We need to put them in place and keep acting collectively. That’s how we will do the best for children.

Keep going!