Effects of wearing FFP2 masks on SARS-CoV-2 infection rates in classrooms

Abstract

Importance: Different mitigation measures are mandated in schools worldwide to control the spread of SARS-CoV-2. The efficacy of most measures, however, has not been investigated thus far. Objective: To investigate the usefulness of FFP-2 masks in classrooms to prevent the spread of SARS-CoV-2. Design: A retrospective comparative cohort study of infection rates (evaluated by PCR screening in school) in students wearing FFP-2 masks continuously and students in sports classes with limited face mask use. Setting: A single-center evaluation comparing classes (middle school: age 10-16 years, 4-year high school: age 14-20 years) with a high sports focus (SF), with regular classes during the Delta and Omicron waves (September 2021-April 2022). Participants: In total, 616 children/families were invited to participate in the comparative evaluation, and 614 (99.7%) followed this invitation by providing relevant information concerning their SARS-CoV-2 infection status. A total of 213 legal guardians (for children < 14 years) and 401 adolescents (14 years and older) reported SARS-CoV-2 infections during the 2021/22 school year. Main Outcomes and Measures: A comparative analysis of cumulative SARS-CoV-2 infection rates in sports and non-sports classes (the 7-day classroom incidence of SARS-CoV-2 infections, and potential secondary infections among school classmates). Results: Cumulative SARS-CoV-2 infection rates were clearly higher in sports classes (with limited mask use) than in non-sports classes (continuous mask use). After the relaxation of the mitigation measures, students in non-sports classes, however, showed a clear catch-up of infections, leading to a higher incidence of infections during this phase. By the end of the observation period (April 30, 2022), only a small difference in cumulative SARS-CoV-2 infection rates (p=0.037, phi=0.09) was detected between classes with a sports focus and those without a sports focus. Conclusions and Relevance: Wearing FFP2 face masks reduces the risk of SARS-CoV-2 infection if strict mitigation measures are applied. Following the relaxation of strict measures, previously protected students show a significant catch-up infection rate. Thus, continuous face mask use postpones rather than avoids SARS-CoV-2 infection in many cases. Therefore, the advantage of reduced transmission must be carefully balanced against the disadvantages associated with mask wearing throughout schools.