Bigger class could mean up to five times the COVID-19 infections, Canadian study suggests

By | August 23, 2020

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The new modelling study, which hasn’t yet been peer-reviewed, was designed to capture transmission of the SARS-CoV-2 virus that causes the dreaded COVID-19. Researchers looked at the effect of different student-to-teacher ratios in a hypothetical primary school, as well as school-based daycare, an essential “bridge” for working parents who can’t drop-off or pick-up kids around the school hours.

Under their most optimistic scenario of masking, social distancing and good hand washing, the model predicted an average of 53 infections during an outbreak in a school community of 150 students, parents and teachers in classes of 30 students, versus 12 infections for classes of 15, where students attend alternative weeks in groups of 15 each.

Outbreaks happened over 40 to 60 days, on average, for the 30-students-to-one-teacher ratio. The number of student-days lost due to classroom closures ranged from 75 for the smallest ratio, to 1,000 for the largest. “Student days are like passenger miles — it’s the number of students affected, times number of days lost,” Bauch said.

School is going to accelerate spread of the virus if it’s already in the community

The model is based on assumptions, including the infectiousness of the virus and how quickly it can spread. It assumed children and teachers are at a “constant background risk of infection from other sources,” like shopping centres. But Bauch explained the math as a “triple whammy.”

“When you put more students in a classroom there is a higher chance one of them will test positive at some point for COVID, and so you’ve got to close that classroom.” The larger the class, the more students affected at a time. But because people can spread COVID before they develop symptoms, “by the time you’ve identified that COVID case there might be other cases in the classroom already,” Bauch said. And, the more kids in a classroom, the trickier the social distancing. “You get aerosol transmission and you generate more cases by the time the classroom gets closed,” he said.

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