Larger class sizes could have dramatic impact on coronavirus transmission: study

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A bigger class size could have a dramatic effect on the number of COVID-19 cases at school, a new study suggests.

Researchers with the University of Waterloo and University of Guelph used a computer model to examine how the virus could spread at primary schools in Ontario and within students’ homes.

Read more: Coronavirus: A guide to back-to-school rules across Canada

They looked at class sizes of eight, 15 and 30. They expected that doubling the class size would mean a doubling of cases, along with a corresponding increase in the number of days classrooms were closed.

But the result was much worse than that, according to lead researcher Chris Bauch.

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“We found that every time we doubled the classroom size, the number of cases and the days of classroom closure, either tripled, quadrupled or even quintupled,” said Bauch, an applied mathematics professor at the University of Waterloo.

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“We also found that this effect was the same, regardless of whether or not infection protocols were in place.”

Read more: Quebec parents file legal challenge against province over back-to-school plan

Why was the increase so dramatic? It’s a bit of a triple-whammy, Bauch said.

If a classroom is larger, there’s a greater likelihood that a COVID-19 case will pop up to begin with. Also, with a larger class size, even more students will be affected by shutdowns related to coronavirus outbreaks.

Social distancing is harder in a room with more people, Bauch said, and there are more aerosols in the air that could heighten the chance of infection.

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“By the time you’ve identified a positive case in the classroom, there might be others already in the classroom that have been spreading quite intensely because they have 30 students in there,” he said.

Read more: Coronavirus cases spiked in reopened U.S. schools. Should Canadians be concerned?

The study has not yet been peer-reviewed but has been submitted for publication. It comes amid intense scrutiny over reopening classrooms this fall, as well as debate over whether measures in place are enough to ward off a resurgence of the virus.

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Provincial health officers are expressing confidence in the plans to protect students.

Earlier this week, Alberta’s top doctor said there hasn’t been a significant amount of transmission for primary school or elementary school-aged children in countries with low virus rates.

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“In Sweden they kept their elementary schools open for the duration of their response to the pandemic. Elementary school teachers in Sweden had a lower risk of getting COVID than the general population … about a 30 per cent lower risk than the general population,” said Dr. Deena Hinshaw.

“And their class sizes were on average over 20 and they did not require distancing in that younger age cohort.”

Neighbouring Finland, which did close its schools, did not experience a lower rate of infection among children, a report from the two countries found last month.

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A patchwork of different plans are in place across the provinces.

Depending on a student’s age and where they live, they might be going back to school in the same size classroom, while others are in smaller classes or learning online part-time.

Read more: Over 500 coronavirus cases connected to public places in Canada since July 4, data shows

In Quebec, where all students are returning to the classroom physically unless they have a medical exemption, a group of parents filed legal action against the provincial government in hopes of securing a distance-learning option.

“Our argument is that fundamental questions of life, death, illness security are ones that belong naturally to the families and not to regulators and that’s what the charter guarantees,” human rights lawyer Julius Grey said Friday.

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Bauch said the researchers felt there wasn’t a lot of “systematic, evidence-based decision making” to guide how school could resume amid the pandemic.

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“And we thought that a model could be useful for giving us insight into how different scenarios could unfold,” he explained.

Recent research from the Public Health Agency of Canada — also based on computer modelling — found that while closing classrooms would indeed reduce the rate of infections within schools, it had far less of an impact on the pandemic overall compared to partial community closures.

Read more: Teachers and students become infected with coronavirus at 41 German schools

While the start of the school year is still weeks away in Canada, classroom reopenings in some parts of the U.S. — where virus transmission is much higher — have resulted in outbreaks.

Schools in at least 10 states have had students and staff test positive for the virus so far. Michigan is reporting 14 outbreaks at schools. Mississippi started the week with about 2,000 students and 600 teachers in quarantine.

That state has had 245 cases of coronavirus in teachers and about 200 in students since districts began returning to school in late July.

— with files from The Associated Press, Kalina Laframboise and Olivia O’Malley, Global News

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