Study protocol: The protective effect of face mask wearing against respiratory tract infections: a pragmatic randomized trial

Abstract Background: Face masks have been strongly advised or mandated in many countries to curb the transmission of respiratory infections during the COVID-19 pandemic. However, the magnitude in risk reduction by wearing face masks in real life settings is still unclear. Randomized trials are needed to examine the effectiveness of face masks on transmission of respiratory viruses in real life settings. Objectives: The primary aim of this study is to examine whether wearing face masks has a protective effect on self-reported tract infection compared with not wearing face mask in public settings in Norway. Methods: This study is a pragmatic, two-armed cluster randomized superiority trial including participants in Norway. Participants will be randomized to one of the following two arms: control group or medical masks in a 1:1 ratio. The intervention is to ask participants in the intervention groups to wear face masks when close to others outside their home, e.g., in public spaces like shopping centres, and streets and on public transport. The control group will be asked not to wear face masks when close to others outside their home, e.g., in public spaces like shopping centres, and streets and on public transport. Participants will continue to use, or not use, face masks at work independent of which group they are allocated to. The study period is 14 days and participants will be asked to complete a baseline and follow-up questionnaire. The primary outcome is self-reported respiratory infection. Secondary outcome are self-reported Covid-19 prevalence and Covid-19 incidence based on registry data. We estimate a need for 1346 participants in each study arm to demonstrate a statistically significant difference (p