Infection and transmission risks in schools and contribution to the COVID-19 pandemic in Germany – a retrospective observational study using nation-wide and regional health and education agency notification data

Abstract

Background Currently, information on infection and transmission risks of students and teachers in schools, the effect of infection control measures for schools as well as the contribution of schools to the overall population transmission of SARS-CoV-2 in Germany is limited to regional data sets restricted to short phases of the pandemic. Methods We used German federal state (NUTS-2) and county (NUTS-3) data from national and regional public health and education agencies to assess infection risk and secondary attack rates (SARs) from March 2020 to October 2021 in Germany. We used multiple regression analysis and infection dynamic modelling, accounting for urbanity, socioeconomic factors, local population infection dynamics and age-specific underdetection to investigate the effects of infection control measures. Results We included (1) nation-wide NUTS-2 level data from calendar weeks (W) 46-50/2020 and W08-40/2021 with 304676 infections in students and 32992 in teachers; (2) NUTS-3 level data from W09-25/2021 with 85788 student and 9427 teacher infections and (3) detailed data from 5 regions covering W09/2020 to W27/2021 with 12814 infections, 43238 contacts and 4165 secondary cases for students (for teachers 14801, 5893 and 472 respectively). In counties with mandatory surgical mask wearing during class in all schools, infection risk of students and teachers was reduced by 56/100,000 persons per 14 days and by 30% and 24% relative to the population, respectively. Overall contribution to population infections of contacts in school settings was 2-13%. It was lowest during school closures and vacation and highest during normal presence class intervals. Infection risk for students increased with age and was similar to or lower than the population risk during second and third waves in Germany and higher in summer 2021. Infection risk of teachers was higher than the population during the second wave and similar or lower thereafter with stricter measures in place. SARs for students and staff were below 5% in schools throughout the study period. SARs in households more than doubled from 14% W21-39/2020 to 29-33% in W08-23/2021. Most contacts were reported for schools, yet most secondary cases originated in households. In schools, staff predominantly infected staff and students predominantly infected students. Conclusions Open schools under hygiene measures and testing strategies contribute up to 13% of nation-wide infections in Germany and as little as 2% during vacations/school closures. Tighter infection control measures stabilised school SARs whilst household SARs more than doubled as more transmissible variants became prevalent in Germany. Mandatory mask wearing during class in all school types effectively reduces secondary transmission in schools, as do reduced attendance class models.

Age-specific contribution of contacts to transmission of SARS-CoV-2 in Germany

“…In the next step, we investigated the contribution of schools to the transmission of SARS-CoV-2 during the third wave in the German population. This is presented in more detail in Heinsohn et al [ 19 ]. Using data reported for schools as well as a school contact matrix, we obtained the estimated forces of infection in schools by age group in Fig.…”

“…Based on information about the cases that are known to have been detected in schools, we estimated the contribution of contacts in schools to be very variable, up to 12% during calendar weeks 10 to 30 in 2021 when schools were open with hygiene measures in place. We expanded these estimations in an analysis performed on surveillance data from public health and educational agencies to the Omicron wave and found contributions of up to 20% to overall population SARS-CoV-2 cases from contacts in schools [ 19 ]. Interestingly, in contrast to what we found for age groups, this estimate was not critically affected by including underdetection estimates.…”