This fall, we once again start a school year during a pandemic. While we have learned many important facts about COVID-19 and how to limit its spread, the circulation of new variants of concern and more specifically of the Delta variant raise questions about sending children to school.
Parents, policy-makers and school administrators are concerned with how society can make the best choices, fine-tune interventions and increase the odds for kindergarten to Grade 12 children to thrive and remain physically and mentally healthy during in-person learning.
With no vaccines yet approved for children under 12, balanced decision-making will be crucial and should be done according to local epidemiology and vaccination coverage.
1. How have SARS-CoV-2 variants spread in schools?
Infections with the Delta variant were detected in British students, but this did not lead to high case numbers. Only 0.27 per cent of primary school pupils tested positive compared to about one per cent in the winter period.
In Québec, where some of our epidemiology research is based, 94 per cent of schools reported cases by April 2021.
An overview of global studies (not all had been peer-reviewed), where the data had been collected after January 2021, suggests there is evidence of transmission in schools and daycares worldwide. Transmission, however, remained limited under a wide range of prevention measures such as masking, cohorting, cancelling higher-risk activities, distancing, hygiene protocols, reduced class size and enhanced ventilation.
Both children and adults have been primary cases in schools — meaning that either children or adults can be the first in a given environment to spread the infection to others. A good way to measure and compare how the infection spreads from primary cases is to calculate the “secondary attack rate” (the number of new cases an initial case infects, per 100 exposed individuals) and to report this rate separately for children and adults. The secondary attack rate can also be compared between settings.
Children who are infected have often been undiagnosed because they are less likely to be tested. Studies that randomly tested school children for an active infection did not detect widespread silent transmission among children and adults in those schools.
Seroprevalence studies, including a Canadian study from Vancouver that is not peer reviewed, have looked for the presence of antibodies following infection, and have shown that children in in-person learning were typically infected at similar rates as other groups in the local community.
School outbreaks have been investigated and reported by researchers and in the media. It can be difficult to identify the origin of the outbreak and its transmission, when many cases are diagnosed at the same time, and without a complete outbreak investigation. Overall, children who had contact with an infected household member had the highest risk of infection. SARS-CoV-2 outbreaks can be related to superspreading events, however, to our knowledge, no superspreading event has been attributed to a young child.
Population studies estimate the Delta variant is two to three times more contagious than the wild strain and 50 per cent more transmissible than the Alpha variant.
2. How are schools stopping the spread of variants and decreasing airborne transmission in schools?
Implementing infection control measures and guidelines is crucial to decrease the risk of transmission in the school environment.
In order to mitigate SARS-CoV-2 transmission, epidemiologists rely on a layered approach of applying timely detection of symptoms and testing, limiting direct contact or distancing, limiting the number of contacts and mixing, ventilation, masking, standard hygiene practices and vaccination. This layered approach is also called the Swiss Cheese Model of infection prevention, where each additional measure prevents further transmission should the virus escape other barriers.
A study, which has not been peer-reviewed, estimates that this layered approach is necessary to control transmission with Delta in kindergarten to Grade 12 schools, as does other research about transmission in university environments.
However, measures must be tailored to local epidemiology and vaccination coverage, and tested for their feasibility (for example, the feasibility of distancing with younger children).
Less attention needs to go to disinfecting and cleaning, because transmission through surfaces or objects is unlikely. The extent to which distancing rules lower the transmission risk depends on additional measurements already in place (like masking and ventilation) and the occupancy of the space.
The focus has shifted to air quality and ventilation in the classroom. Some schools changed the quality of air filters they use in mechanical systems or distributed portable HEPA filters. Others pledged to install carbon dioxide monitors.
3. Should schools test students for COVID-19?
Because there were insufficient data on mask use and effectiveness in young children, masks were inconsistently implemented in Europe and the U.K. when the pandemic was hitting hardest in 2020-21.
It is difficult to measure the impact of masks in schools in particular. We do know that mask wearing among adults reduces COVID-19 cases, and also reduces mortality. Masks are a potent tool against transmission, but a mask-wearing mandate alone is not enough.
Masks also protect children from other respiratory infections, which have been circulating again since the spring. The extra barrier can decrease the spread of many other viruses, and may decrease the amount of time students spend out of school because of symptoms that cannot be distinguished from those of COVID-19 and will lead to testing and quarantines.
Testing has been used in schools to diagnose cases, in outbreak investigations, for quarantine guidance and as prevention. Tests can, for example, be applied to decrease the duration of quarantine. Tests can also be used to prevent students and teachers from coming to school when they are infectious.
Repetitive, weekly and bi-weekly testing has been used as an additional layer of protection. However, the burden and costs related to the testing are large, especially when the community incidence is low and only low numbers of cases can be picked up. A more realistic option would be to randomly choose some schools to monitor viral circulation across the country.
Whether testing is used for preventive screening or for diagnosis, it is crucial that samples are collected in a child-friendly way, for example, using gargle samples, spit or saliva. The tests should be equally accessible and readily available for the family, and the results be rapidly available to decrease time in uncertainty.
The type of tests made available for children should also have few false positives, so that we don’t isolate children who are no longer carrying infectious virus.
Another concern is children who are tested and receive a false negative result (the test says negative, but they’re actually positive). Both testing errors have a disruptive effect and cause harm. What’s needed is easy, accessible and frequent testing with a modestly sensitive but highly specific test.
Vaccination remains the most effective direct and sustainable prevention against infectious diseases. Vaccine mandates and other initiatives encouraging vaccines to increase vaccine coverage in schools of all who are eligible — teachers and older children — seem to be the most valuable strategies to decrease transmission.
4. What best practices of infection prevention and control should schools follow?
The set of mitigation practices described in Question No. 3 are implemented in most countries. There are, however, major differences in the intensity, method, co-ordination, communication and measurement of their implementation and their feasibility.
In terms of mass vaccination, Canada is one of the fortunate countries to have this implemented broadly. Some countries around the globe have not been as fortunate.
Many countries developed guidelines for infection prevention and control measurements, often prescribed by public health and ministries of education.
Advice from pediatric medical societies and their experts has been integrated in some of the guidelines. The European Centre for Disease Prevention and Control provides an overview of mitigation guidelines, as do the Centers for Disease Control and Prevention in the United States and the World Health Organization.
The Government of Canada made a guideline document available, while the provinces are providing local guidelines.
Even among the neighbouring European countries of Belgium, the Netherlands and Luxembourg, the measures differ. Masks, for example, are mandatory in primary school in Luxembourg unless students are sitting more than 1.5 metres apart in classrooms, which is feasible because there is a maximum of 15-18 pupils per classroom there. Masks are mandatory at all times inside primary schools in France, but not in Belgium or the Netherlands. Rules for quarantine also differ in those countries.
Of course, experts’ recommendations do not always align with political decisions.
This fall, policy-makers and school leaders must continue to deploy preventive measures in schools in an equitable manner. Parents, older children and all community members who are eligible for vaccination have a role to play by becoming vaccinated. They can also listen to children’s voices and experiences as children enter a challenging school year — and seek to understand and practise their own roles in keeping one another healthy.