Social network-based cohorting to reduce the spread of SARS-CoV-2 in secondary schools: A simulation study in classrooms of four European countries

Abstract

Background Operating schools safely under pandemic conditions is a widespread policy goal. We analyse the effectiveness of classroom cohorting, i.e., the decomposition of classrooms into smaller isolated units, in inhibiting the spread of SARS-CoV-2 in European secondary schools and compare different cohorting strategies. Methods Using real-world network data on 12,291 adolescents collected in classrooms in England, Germany, the Netherlands, and Sweden in 2010/2011, we apply agent-based simulations to compare the effect of forming cohorts randomly to network-based cohorting. Network-based cohorting attempts to allocate out-of-school contacts to the same cohort to prevent cross-cohort infection more effectively. We consider explicitly minimizing out-of-school cross-cohort contacts, approximating this information-heavy optimization strategy by chained nominations of contacts, and dividing classrooms by gender. We also compare the effect of instructing cohorts in-person every second week to daily but separate in-person instruction of both cohorts. Findings We find that cohorting reduces the spread of SARS-CoV-2 in classrooms. Relative to random cohorting, network-based strategies further reduce infections and quarantines when transmission dynamics are strong. In particular, network-based cohorting inhibits superspreading in classrooms. Cohorting that explicitly minimizes cross-cohort contacts is most effective, but approximation based on chained nominations and classroom division by gender also outperform random cohorting. Every-second-week instruction in-person contains outbreaks more effectively than daily in-person instruction of both cohorts. Interpretation Cohorting of school classes can curb SARS-CoV-2 outbreaks in the school context. Factoring in out-of-school contacts can achieve a more effective separation of cohorts. Network-based cohorting reduces the risk of outbreaks in schools and can prevent superspreading events. Funding None.

Effectiveness of social distancing measures and lockdowns for reducing transmission of COVID-19 in non-healthcare, community-based settings

“…Another ecological study examining schools in North Carolina and Wisconsin, US, from 2020 to 2021 did not observe an increase in the secondary transmission rate in schools after distancing measures were relaxed, indicating they had no effect on transmission in these schools [ 149 ]. The remaining simulation studies found that school measures were associated with reductions in public health impacts of COVID-19, both in the schools [ 156 – 158 , 160 , 162 – 166 ] and the community [ 155 , 159 , 161 ].…”

“…Eighteen included studies estimated the effectiveness of school measures (not including closures) to reduce the impact of COVID-19. Six were observational studies [149][150][151][152][153][154] and 12 were simulation studies [155][156][157][158][159][160][161][162][163][164][165][166]. Most studies were carried out in 2020 at a sub-national scale (electronic supplementary material, appendix C).…”

Considerations for the Safe Operation of Schools During the Coronavirus Pandemic

“…Computational modeling suggests that weekly rotations (i.e., 5 days in school, 5 days remote) or groups of students rotating 2–3 days in school every week limit the number of contacts between students and teachers to reduce the likelihood of transmission events in schools ( 161 , 210 ). Existing out-of-school social networks among students may guide such cohort formation and lead to a more effective reduction of contacts ( 211 ). However, whether these predictions translate into measurable effects on secondary cases in schools remains to be tested.…”

Quantifying pupil-to-pupil SARS-CoV-2 transmission and the impact of lateral flow testing in English secondary schools

“…A parallel study by Kunzmann et al considered the impact of such measures in primary schools, reaching a similar conclusion that serial contact testing alone would be insufficient to contain outbreaks, recommending a combination of mass testing and isolation of close contacts 27 . Other studies have explored the impact of alternative within-school control measures, such as PCR-based testing strategies 28 , dividing classes into discrete cohorts 29 , 30 , and mask-wearing 31 . Owing to the paucity of information surrounding SARS-CoV-2 transmission rates between children within schools, such studies typically consider a range of pupil-to-pupil transmission rates.…”