Regular rapid tests detect COVID-19 early enough to stop transmission in schools

Proactive and frequent rapid testing of all students for COVID-19 is more effective in preventing large transmission clusters in schools than measures that are only initiated when a person develops symptoms and then tests positive, have found. researchers from Simon Fraser University. Professors Caroline Colijn and Paul Tupper used a mathematical model to simulate the spread of COVID-19 in the classroom and published their research results today in the journal Computational biology PLOS.

Simulations showed that in a classroom of 25 students, zero to 20 students could become infected after exposure, depending on even small adjustments in transmission rates for infected individuals or environments.

“When schools reopened during the COVID-19 pandemic, in some places there were large clusters of infections and in others very little transmission,” says Colijn, professor of mathematics at SFU and chair of Canada 150 research in mathematics for evolution, infection and the public. Health. “In our simulations, we explored what factors affect cluster size and what interventions can be used to prevent large clusters. “

Researchers tested the effectiveness of two different transmission control strategies.

In the first, when a student (or teacher / staff member) develops symptoms, they are told to stay home, tested using a PCR test, and if the test result is positive, control measures are introduced in the classroom, such as telling close contacts of the infected person to stay at home.

In the second strategy, all students in the class are tested regularly using rapid tests, whether or not they have symptoms. When a student tests positive, there is intervention to prevent further transmission.

The researchers found that in scenarios with high transmission rates, the interventions used in the first control strategy, where preventive actions took effect after a positive test result, were too slow to prevent large outbreaks. The use of rapid tests to screen the entire population and detect infections before symptoms appear, as in the second strategy, has prevented major epidemics.

“We found that interventions that took effect only after a person had developed symptoms and tested positive were too slow to prevent large clusters; only regular monitoring of asymptomatic people could prevent worse outcomes,” says Colijn .

Their study is timely, as British Columbia is set to enter Stage 4 of its reopening in September and concerns remain about a resurgence of COVID-19 in the fall. Regular testing for COVID-19 in the form of rapid tests has not been widely used in schools in British Columbia, although Alberta and Saskatchewan plan to roll out rapid tests to schools in the fall. , and Nova Scotia has long embraced rapid testing in a variety of settings. .

Tupper says they hope to use data on transmission and cluster size in schools to estimate key unknowns about COVID-19 in schools, such as the rate of transmission and how much it varies from classroom to classroom. the other.

“We could then see how transmission depends on the preventive measures that are put in place, such as mask use, improved ventilation and hand washing,” he says. “This would indicate which interventions, after a case is detected, would be the most effective.”

The research results could be applied to other settings where people spend several hours a day with the same group of about 20 to 30 other people.

“Our results were based on classroom simulations, but the same considerations apply to other settings such as workplaces or community living settings such as long-term care homes,” explains Tupper, noting that their previous work underscores the effectiveness of rapid tests in protecting residents of long-term care homes.

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Tupper’s research was funded by a Discovery Grant from NSERC (Canada). Colijn was supported by a grant from Genome BC (COV142) and the Canada 150 Research Chairs program of the federal government of Canada. The researchers also thank Covid Écoles Québec for the data on the size of clusters in schools in Quebec.

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