A modeling study on SARS-CoV-2 transmissions in primary and middle schools in Illinois

The global pandemic caused by the SARS-CoV-2 virus led to a statewide lockdown in Illinois starting in March 2020. To ensure students' and employees' safety for school reopening, protective measures, such as a statewide mask mandate and weekly testing, were in place in Illinois from Spring 2021 to Spring 2022. The study objective is to 1) estimate the in-school and external transmission of SARS-CoV-2 in elementary and middle schools under mask mandate and weekly surveillance and 2) estimate the impacts of protective measures such as testing and mask proportion and testing frequency on SARS-CoV-2 transmission.

A stochastic compartmental model was built to simulate the SARS-CoV-2 transmission within and between the student and employee groups in primary and middle schools participating in the weekly testing program and to evaluate the effectiveness of these protective measures. This stochastic model was modified from a susceptible-infected-recovered framework and calibrated to SARS-CoV-2 surveillance data in 116 primary and middle school districts from Spring 2021 to March 2022. This model calibration was assessed using the surveillance data from the rest of the spring semester in 2022.

Overall, the external transmission rates in students and employees were significantly greater than those within schools, and the external transmission rates in middle school students and school employees were greater than those in primary school students. Our sensitivity analysis showed that transmission rates within student groups could significantly influence overall infection rates in vaccinated and unvaccinated students in large school districts. Under the protective measures implemented in the studied period in Illinois, an increased proportion of students and employees participating in the weekly testing can decrease infections. However, community-level measures of self-reported mask adherence among adults were not significantly associated with the infections during the study period, when a universal mask policy was in place for the state.

Although increased testing proportion and/or frequency can reduce the SARS-CoV-2 infections, the costs of testing can increase with the testing volume. Further studies on the cost-effectiveness between the testing volume and cases reduction or learning disturbance can aid in policy development to reduce transmission effectively.