Variation in SARS-CoV-2 seroprevalence across districts, schools and classes: baseline measurements from a cohort of primary and secondary school children in Switzerland

Objectives To determine the variation in SARS-CoV-2 seroprevalence school children and relationship with self-reported symptoms. Design Baseline measurements of a longitudinal cohort study ( Ciao Corona ) from June to July 2020. Setting 55 schools stratified by district canton Zurich, Switzerland. Participants 2585 (1339 girls; median age: 11 years, age range: 6–16 years), attending grades 1–2, 4–5 7–8. Main outcome measures Variation across 12 cantonal districts, grades, assessed using Luminex-based test four epitopes for IgG, IgA IgM (Antibody Coronavirus Assay,ABCORA 2.0). Clustering cases within classes. Association seropositivity Comparison adult population, IgG (Sensitive Anti-SARS-CoV-2 Spike Trimer Immunoglobulin Serological test). Results Overall was 2.8% (95% CI 1.5% 4.1%), ranging 1.0% 4.5% districts. Seroprevalence 1–2 3.8% 2.0% 6.1%), 2.4% 1.1% 4.2%) 7–8 0.5% 3.0%). At least one seropositive child present 36 (65%) 44 (34%) 131 classes where ?5 ?50% class were tested. 73% reported COVID-19-compatible symptoms since January 2020, same frequency seronegative all adults similar (3.2%, 95% credible interval (CrI) 1.7% 5.0% vs 3.6%, CrI 5.4%). The ratio confirmed cumulative incidence-to-seropositive 1:89 1:12 adults. Conclusions low that end Very diagnosed-to-seropositive observed. We did not detect clustering SARS-CoV-2-seropositive classes, but follow-up this will shed more light on transmission schools. Trial registration number NCT04448717 .