A new Canadian study shows how SARS-CoV-2 transmission has occurred in schools


In a recent study published on the prepress server medRxiv *, Researchers from Canada studied the frequency, size of the cluster and the rate of transmission of coronavirus disease (COVID-19) in schools using a simple mathematical model.

study: COVID-19 clusters in schools: frequency, size and transmission rate from crowdsourcing exposure reports. Image credit: Prostock-studio / Shutterstock.com

SARS-CoV-2 transmission in schools

Current data on the role of schools in the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus responsible for COVID-19, are conflicting. Although COVID-19 in children is usually not as severe as in adults, the risk of multisystemic inflammatory syndrome in children (MIS-C) is alarming. In addition, the spread of SARS-CoV-2 through schools may indirectly expose vulnerable groups to the risk of infection and thus affect the safety of the whole community.

More studies are needed to determine the involvement of schools in accelerating the transmission of SARS-CoV-2, as previous studies do not provide significant data on the role of schools.

About the study

The present study uses a summary model to determine the heterogeneity of COVID-19 transmission rates in schools and cluster size variations between 2020-2021 in four Canadian provinces and eight US states. Data for Canada were collected by COVID Schools Canada, and data for the United States were obtained from the National Education Association’s website. The study also assesses the parameters of over-variance of different jurisdictions and their averages.

The data collected include the name of the school, the number of infected students and the date of the report. In Canada, generally positive cases were included, including staff and teachers, while in the United States only confirmed cases of students were included.

Establishment factions were estimated using estimates of the variance parameters that were used to determine the uneven distribution of cases between different clusters of jurisdiction, the fraction present in 20% of the largest clusters, the time required to obtain a specific the size of the cluster in the jurisdiction, and the distribution of the baud rate (β) between different cases of the index. The authors were unable to distinguish between SARS-CoV-2 transmission, which occurs in schools, and what occurs during children’s social activities outside of school.

Survey results

Based on the results, Canada has a larger number of clusters, which may be due to their long data collection period. The state-wide incidence rate is higher in the United States. This difference may be due either to the reduced likelihood of reporting smaller clusters or to incomplete data.

Canada has a lower observed variance than the United States, as the estimated average cluster size of different jurisdictions in the study ranges from 1.3 to 1.7 cases in Canada and 2-8 cases in the United States. clusters of cases can cause an upward deviation in cluster size, and fewer cases found in a cluster of multiple cases can lead to a downward deviation.

Using a simple classroom transmission model, the contact time transmission rate per unit time was calculated. The results of the study can be used to estimate the time required to observe a larger cluster in a given jurisdiction. Estimates range from five days to more than 50 days for the different jurisdictions in the study.

The study did not focus on transmission information at the individual level or the average cluster size of COVID-19; however, using the distribution of a random Poisson variable for the cluster size and the main gamma-distributed random variable, the transmission rate β was determined.

The effects of social distancing, masking and bubbling (keeping the contact list constant) were also studied. To this end, masking and class size reduction were found to be much more effective in reducing cluster size than bubbling.

(Top) Estimates of the percentage of new clusters reported in each jurisdiction as a function of time in 8 U.S. states (left) and 4 Canadian provinces (right).  (Below) Incidents per day in the same jurisdictions during the relevant time interval.
(Top) Estimates of the percentage of new clusters reported in each jurisdiction as a function of time in 8 U.S. states (left) and 4 Canadian provinces (right). (Below) Incidents per day in the same jurisdictions during the relevant time interval.

Conclusions

The authors propose a simple model that uses cluster size data to obtain information on the average size, transmission rate, and frequency of COVID-19 across schools from data stored in public health facilities without requiring contact or data tracking. at the individual level. The study reports that the majority of school broadcasts take place in a small number of classrooms, with 20% of the largest clusters having about 80% -100% of the average.

For each jurisdiction, the expected number of days to observe a cluster of a given size or larger in the dataset.
For each jurisdiction, the expected number of days to observe a cluster of a given size or larger in the dataset.

The present study developed a method for detecting the rate of transmission from individuals to individuals from cluster size data. In addition, the findings discussed here emphasize the importance of data collection in determining cluster size.

The approach used in this study can be summarized to compare other settings such as workplace outbreaks. In addition, these data help reduce SARS-CoV-2 transmission related to school or the workplace by providing effective intervention projects.

Most children 12 years of age or older in the U.S. and Canadian jurisdictions surveyed were vaccinated in 2021, as were the general population. This will lead to fewer cases of COVID-19 in general, fewer exposures in schools and fewer clusters. However, the emergence of more infectious dangerous variants of SARS-CoV-2 such as the Alpha, Delta and Omicron variants may lead to the resurgence of clusters.

*Important message

medRxiv publishes preliminary scientific reports that are not reviewed by partners and therefore should not be considered convincing, guiding clinical practice / health-related behavior, or treated as established information.



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