Table 2.

Summary of Evidence of Impact of Cohorting/“Bubble” Formation to Minimize Student Interaction in School Settings

Study/Country	Setting	Study Type	Cohorting Intervention	Simultaneous Interventions	Results	Data Source
Brandal et al. [103], Norway [60, 62]	Primary schools in Oslo & Viken, grades 1–7	Cohort study, examined transmission in students who attended school within 48 h with tracing/testing of contacts twice during quarantine period, Aug–Nov 2020	Established small, fixed groups (15 & 20 maximum class size in primary & middle schools, respectively)	Masks not recommended	Minimal child-to-child (0.9%, 2/234) and child-to-adult (1.7%, 1/58) transmission	Department of Virology at the Norwegian Institute of Public Health, Norwegian Surveillance System for Communicable Diseases
Denmark [61, 62]	Child care & primary education settings	European Centre for Disease Prevention and Control (ECDC) report, nationwide surveillance	Split classes into small groups (bubbles) of 10–11 students [7]; first phase re-opening, children ≤12 y, Apr 15, 2020	Physical distancing 2 m; masks not recommended	Did not report an increase in the reproductive number or detect important school outbreaks after re-opening; published Aug 6, 2020	The European Surveillance System (TESSy)
Ismail et al. [104], England [66]	Early years settings, primary schools, & secondary schools	Cross-sectional analysis, estimated rate of infection & outbreaks during summer half-term, Jun–Jul 2020	Classes small & separated into distinct social bubbles that perform all activities together and do not mix with other bubbles	Maintain distance as able between children and 2 m between adults	Median daily student attendance 928K. Median of 38K early year settings (age <5), 15.6K primary schools (age 5–11), and 4K secondary schools (age 11–18) open daily. Infections & outbreaks low. 113 single cases of infection, 9 coprimary cases, and 55 outbreaks.	Public Health England
Isphording et al. [105], Germany	Schools in all German states	Event study analysis, evaluated effect of end of summer break and school re-opening on pandemic spread, Aug–Sep 2020	Fixed groups were assigned on classroom or cohort basis, remaining physically separated, often with staggered school start times	Masks mandatory	Three weeks after end of summer breaks, relative numbers of new cases gradually decreased (0.55 cases per 100K inhabitants) in re-opening states relative to those not yet re-opening.	Robert-Koch-Institute
Link-Gelles et al. [32], USA	Child care programs in Rhode Island	Cohort study, investigated COVID-19 cases at child care programs, Jun 1–Jul 31, 2020	Initially maximum 12 persons including staff members in stable groups; increased to 20 persons on Jun 29	Masks mandatory for adults	666 of 891 programs re-opened. 33 confirmed child care–associated cases & 19 probable child care–associated cases. 30 cases in children with median age 5 y. 39 cases occurred from mid- to late July when state incidence was increasing. Cases occurred in 29 programs, 20 (69%) of which had a single case without secondary transmission.	Rhode Island Department of Health

Abbreviations: COVID-19, coronavirus disease 2019; ECDC, European Centre for Disease Prevention and Control; TESSy, The European Surveillance System.