Proactive vs. reactive COVID-19 screening in schools: Lessons from experimental protocols in France during the Delta...

The COVID-19 pandemic prompted diverse policies to manage safety in schools, balancing transmission control with educational continuity. We evaluated an experimental weekly screening protocol through salivary PCR tests against nationally implemented reactive strategies (class closure or class screening following case detection) 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 of severe acute respiratory syndrome coronavirus 2 transmission in schools, parameterized with empirical contact data and fitted to observed prevalence in 18 schools selected for the analysis under variant-specific epidemiological conditions. We simulated the weekly screening following the experimental protocol, with 7-day isolation of positive cases and class closure after three detected cases. We quantified reductions in within-school transmission and student-days lost and combined efficacy. The experimental weekly screening protocol reduced within-school transmission by 40% (interquartile range [IQR] 18-53%) during the Delta wave and 39% (IQR 31-46%) during the Omicron wave, relative to reactive strategies implemented nationally. Across both waves, weekly screening without class closure achieved the greatest overall efficiency, balancing transmission reduction and educational continuity. By mitigating asymptomatic spread through a structured and predictable testing schedule, weekly screening offered operational advantages over reactive strategies. These findings explicitly quantify key trade-offs between infection control and educational continuity and inform the design of proactive school-based interventions in future pandemics.