Risking Student Infection in Return to School

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"As you double the class size, from eight to 15 to 30, the number of cases and also the lost student days of instruction not only double each time, they triple or quadruple or quintuple. Those losses accelerate as you go to larger and larger classes."        "[Policy makers planning for elementary school class sizes of 30 kids or more] need to immediately reconfigure their school opening plans [to switch to hybrid models of part in-person, part online]."                                                                                  "Student days are like passenger miles -- it's the number of students affected, times number of days lost. When you put mores 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. By the time you've identified that COVID case there might be other cases in the classroom already.You get aerosol transmission and you generate more cases by the time the classroom gets closed."                    "Many people may infect only one person, or even no one, but in some cases you have a so-called super-spreader who infects a huge number of people."                   Chris Bauch, mathematician, professor of mathematics, Waterloo University

"School is going to accelerate spread of the virus if it's already in the community. This is the same thing that happened when we reopened stores and restaurants. [School reopening] is not going to create more virus, but it's going to make it easier for the virus to spread."                                                                                          "It's very possible you could see cases."                                                        Dr.Chris Labos, cardiologist, epidemiologist, Montreal

A new study undertaken by mathematics professor Dr.Chris Bauch and collaborators to determine the ideal class size in preventing COVID outbreaks affirmed through modelling that the very size classes many provinces are contemplating for their September school reopenings will predict the numbers of infections of COVID-19 certain to break out in each community. The infection numbers will be analogous to the size of classes in primary school classrooms as well as before-and-after school daycare programs.

Universally, teachers in British Columbia, Alberta, Quebec and Ontario are all making demands to their governments to mandate smaller class sizes in fear of just such scenarios unfolding with the reopening of the new school year. Students attending kindergarten to Grade 8 are set in Ontario to return to school with no reduction planned in class sizes. They are scheduled to spend the school day in a single group, limiting contact with other children in their school 'bubble'. Masks are required in grades 4 to12 only.

As a test instance, experts view what has happened in Israel as high schools reopened in May, when weeks afterward, major COVID-19 cases began spiking. In Berlin, hundreds of students and teachers from dozens of schools were infected with the coronavirus; now are in quarantine, two weeks following their school reopenings. 

Researchers who designed the new modelling study looked at the effect of different student-to-teacher ratios in a primary school class, along with school-based daycare to obtain an understanding of transmission of the SARS-CoV-2 virus causing COVID-19.  Despite masking, social distancing and hand washing, the model predicted an average of 53 infections in a school community of 150 students, parents and teachers in classes of 30 students.

Classes of 15, on the other hand, saw viral outbreaks of 12 infections, where students attend alternative weeks in groups of 15 students each class. For the 30-students-to-one-teacher ratio, outbreaks occurred over 40 to 60 days on average resulting in the number of student-days lost as a result of classroom closures ranging from 75 for the smallest ratio to 1,000 for the largest. 

The larger the class the greater number of students affected; the more students to a classroom the more difficult social distancing becomes to achieve.

According to the modelling, the teacher occasionally would be the first to become infected, though more generally it would be a student "because there are more of them. They bring it in somehow and we model what happens -- where they spread it in their household and where they spread it in school." It remains unclear as yet how efficient children are in spreading the virus causing COVID-19. 

As for childcare, the 15 children to two teachers ratio appeared the worst across all possible scenarios. Childcare optimally would be operating on a seven or eight children per room model, according to Dr.Bauch's mathematical reasoning, which would see siblings grouped together in daycare. 

Students at a Berlin high school practise hand disinfection, August 10, 2020. Researchers have explored how different combination of class sizes and time in class could affect potential COVID-19 outbreaks. Fabrizio Bensch/Reuters