Proactive vs. reactive COVID-19 screening in schools: lessons from experimental protocols in France during the Delta and Omicron waves

Abstract The COVID-19 pandemic prompted diverse policies to manage safety in schools, balancing infection control with educational continuity. This study assessed the impact of an experimental weekly screening protocol compared to nationally implemented reactive strategies in 25 primary schools in the Auvergne-Rhône-Alpes region of France during the Delta (November–December 2021) and Omicron (January–February 2022) waves. We used an agent-based model for SARS-CoV-2 transmission in schools parameterized with empirical data characterizing school contact over time to estimate the contribution of school transmission on overall cases and evaluate the effectiveness of weekly screening in reducing within-school infections. We parametrized the model to reproduce the Delta and Omicron variants dominant in the study period, accounting for introductions from community surveillance data. We fitted the model to the observed prevalence in 18 schools selected for the analysis. School transmission was estimated to account for 67% (IQR 53-78) of student cases in Rhône and 67% (IQR 50-82) in Savoie during the Delta wave, and 52% (IQR 47-57) in Rhône during the Omicron wave. The experimental weekly screening protocol was estimated to reduce transmission in school by 40% (IQR 18 – 53%) during the Delta wave and by 37% (IQR 30-45) during the Omicron wave, compared to the reactive strategies applied in the same period in the rest of the country. Adherence rates exceeding 80% during the study were critical to the protocol’s success, contributing to an earlier and sustained decline in prevalence. Weekly screening proved a more structured and effective approach to controlling transmission, supporting its inclusion in future pandemic preparedness plans to ensure safer learning environments. This study underscores the importance of proactive interventions to address asymptomatic spread in schools, emphasizing their role in pandemic response strategies. Competing Interest Statement The authors have declared no competing interest. Funding Statement This study was partly funded by Agence Nationale de la Recherche project DATAREDUX (ANR-19-CE46-0008-03), EU Horizon 2020 grant MOOD (H2020-874850; paper catalogued as MOOD 125), Horizon Europe grants VERDI (101045989) and ESCAPE (101095619). The contents of this publication are the sole responsibility of the authors and don't necessarily reflect the views of the European Commission. Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Contact studies were approved by the Commission Nationale de l'Informatique et des Liberéts (CNIL, the French national body responsible for ethics and privacy) and school authorities. Informed consent was obtained from participants or their parents if minors. No personal information of participants was associated with the RFID identifier. No ethical committee was required for this study as no individual data were collected in the study. All data retrieved during the screening campaign were anonymous and aggregated at the school level. Oral and written consent were obtained from parents ahead of the campaign. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes Footnotes Data Availability De-identified individual data on contacts of the primary school under study are publicly available at the SocioPatterns project website. De-identified aggregated COVID-19 community surveillance data by age class are publicly available at SpF data observatory platform. De-identified aggregated COVID-19 prevalence data from experimental weekly screenings used in this study are contained in the manuscript.