Passing the Test: A Model-Based Analysis of Safe School-Reopening Strategies

Abstract

Background: The COVID-19 pandemic has induced historic educational disruptions. In April 2021, about 40% of U.S. public school students were not offered full-time in-person education.

Objective: To assess the risk for SARS-CoV-2 transmission in schools.

Design: An agent-based network model was developed to simulate transmission in elementary and high school communities, including home, school, and interhousehold interactions.

Setting: School structure was parametrized to reflect average U.S. classrooms, with elementary schools of 638 students and high schools of 1451 students. Daily local incidence was varied from 1 to 100 cases per 100 000 persons.

Participants: Students, faculty, staff, and adult household members.

Intervention: Isolation of symptomatic individuals, quarantine of an infected individual's contacts, reduced class sizes, alternative schedules, staff vaccination, and weekly asymptomatic screening.

Measurements: Transmission was projected among students, staff, and families after a single infection in school and over an 8-week quarter, contingent on local incidence.

Results: School transmission varies according to student age and local incidence and is substantially reduced with mitigation measures. Nevertheless, when transmission occurs, it may be difficult to detect without regular testing because of the subclinical nature of most children's infections. Teacher vaccination can reduce transmission to staff, and asymptomatic screening improves understanding of local circumstances and reduces transmission.

Limitation: Uncertainty exists about the susceptibility and infectiousness of children, and precision is low regarding the effectiveness of specific countermeasures, particularly with new variants.

Conclusion: With controlled community transmission and moderate mitigation, elementary schools can open safety, but high schools require more intensive mitigation. Asymptomatic screening can facilitate reopening at higher local incidence while minimizing transmission risk.

Primary funding source: Centers for Disease Control and Prevention through the Council of State and Territorial Epidemiologists, National Institute of Allergy and Infectious Diseases, National Institute on Drug Abuse, and Facebook.

Visual Abstract.. Model-Based Analysis of Safe School-Reopening Strategies.

The COVID-19 pandemic has induced historic disruptions in education. This agent-based network model simulated transmission in elementary and high school communities, including home, school, and interhousehold interactions.

Appendix Figure.. Model diagram.

The model includes 3 primary domains (households, schools, and out-of-school social or childcare mixing) and incorporates a range of interventions to prevent or reduce transmission.

Figure 1.. Average number of total secondary transmissions over 30 days (outside the index case patient's household) after a single introduction into a school.

This figure displays the average number of secondary transmissions over 30 days following a single case introduction into a school. Estimates include both transmission directly from the index case and that from secondary and tertiary cases. The top panel shows elementary schools, where children are assumed to be less susceptible and less infectious than adults, and the bottom panel shows high schools. Note that axes differ across rows. The x-axes vary the level in-school mitigation with “low” assuming minimal interventions and “high” assuming intensive interventions. A/B = hybrid. (This is not an estimate of the effective reproduction number [Rt], which is shown in Supplement Figures 9 and 10.)

Figure 2.. Distribution of secondary transmissions when a single case is introduced.

The figure displays the distribution of secondary transmissions (outside the index case patient's household) when a single case is introduced into a school. The x-axis varies the level of in-school mitigation with “low” assuming minimal interventions and “high” assuming intensive interventions. Transmissions include both those directly from the index case and those from secondary and tertiary cases. Distributions are truncated at the 99.5th quantile (i.e., all outcomes occur with a probability ≥1/200). A/B = hybrid.

Figure 3.. Cumulative incidence over 8 weeks in elementary schools.

The x-axis shows the average daily local incidence per 100 000 persons in the population. The y-axis shows cumulative incidence over 8 weeks in the elementary school community. Columns denote isolation, quarantine, vaccination, and detection strategies, and rows show population subgroups. We mark a strategy with a point if it fails to meet the transmission control threshold for the subgroup (i.e., if there is a >1-point increase over remote learning in the percentage of the subgroup infected during 8 wk). A/B = hybrid.

Figure 4.. Cumulative incidence over 8 weeks in high schools.

The x-axis shows the average daily local incidence per 100 000 persons in the population. The y-axis shows cumulative incidence over 8 wk in the high school community. Columns denote isolation, quarantine, vaccination, and detection strategies, and rows show population subgroups. We mark a strategy with a point if it fails to meet the transmission control threshold for the subgroup (i.e., if there is a >1-point increase over remote learning in the percentage of the group infected during 8 wk). A/B = hybrid.