Background Data suggest that COVID-19 transmission in K-12 schools is uncommon, but few studies have confirmed this using widespread screening of asymptomatic individuals.

Objective To evaluate the incidence of asymptomatic COVID-19, document the frequency of in-school transmission, and confirm feasibility of widespread asymptomatic screening in schools.

Design Prospective observational study

Setting Single mid-sized suburban school district including 10 schools and a central office.

Participants District staff and students

Interventions Asymptomatic screening PCR for SARS-CoV-2

Measurements Concurrent with a hybrid model and layered mitigation, weekly pooled testing of staff and secondary students was offered using saliva samples collected at home. Identification of >1 case in a school prompted investigation for possible in-school transmission. Staff and families were surveyed about satisfaction with the screening program.

Results From weeks 1-18, rates of incident COVID-19 in the surrounding community rose steadily. Weekly staff and student screening identified 0-7 asymptomatic cases/week. In week 7, 5 cases were identified among staff who shared an office setting. Enhancements to mitigation strategies were undertaken. The proportion of survey respondents self-reporting comfort with in-person learning before versus after implementation of screening increased.

Limitations Because screening testing was not mandatory, the results from the participating population might not represent the entire school community.

Conclusions In this school district with layered mitigation measures, in-school transmission was rare. The program identified a cluster with in-school staff-to-staff transmission and spurred enhancement of safety strategies. A weekly COVID-19 screening program can provide critical data to inform mitigation efforts, and provides school-specific, current data to inform decisions about in-person learning models. Screening provided reassurance and identified asymptomatic cases.

Funding The Wellesley Education Foundation provided funding for the testing.