COVID-19 transmission in educational institutions August to December 2020, Rhineland-Palatinate, Germany: a study of index cases and close contact cohorts

Schoeps, A.; Hoffmann, D.; Tamm, C.; Vollmer, B.; Haag, S.; Kaffenberger, T.; Ferguson-Beiser, K.; Kohlhase-Griebel, B.; Basenach, S.; Missal, A.; Hoefling, K.; Michels, H.; Schall, A.; Kappes, H.; Vogt, M.; Jahn, K.; Baernighausen, T.; Zanger, P.

Background The lack of precise estimates on transmission risk hampers rational decisions on closure of educational institutions during the COVID-19 pandemic. Methods Secondary attack rates (SARs) for schools and day-care centres were calculated using data from state-wide mandatory notification of SARS-CoV-2 index cases in educational institutions and additional information on routine contact tracing and PCR-testing. Findings From August to December 2020, every sixth of overall 784 independent index cases caused a transmission in educational institutions (risk 0.17, 95% CI 0.14-0.19). In a subgroup, monitoring of 14,594 institutional high-risk contacts (89% PCR-tested) of 441 index cases revealed 196 secondary cases (SAR 1.34%, 1.16-1.54). Transmission was more likely from teachers than from students/children (incidence risk ratio [IRR] 3.17, 1.79-5.59), and from index cases in day-care centres (IRR 3.23, 1.76-5.91) than from those in secondary schools. In 748 index cases, teachers caused four times more secondary cases than children (1.08 vs. 0.25 secondary cases per index, IRR 4.39, 2.67-7.21). This difference was mainly due to common transmission from teacher index cases to teacher contacts (mean secondary cases 0.56 teacher to teacher vs. 0.04 child to teacher, IRR 13.3, 6.6-26.7). Interpretation In educational institutions, the risk of contacts to a confirmed COVID-19 case for infection is one percent, but varies depending on type of institution and index case. Hygiene measures targeting the day-care setting and teacher-to-teacher transmission are priorities in reducing the burden of infection and may promote on-site education during the pandemic.