Publication date: Jul 24, 2024

To evaluate the personal protective effects of wearing versus not wearing surgical face masks in public spaces on self-reported respiratory symptoms over a 14 day period. Pragmatic randomised superiority trial. Norway. 4647 adults aged ≥18 years: 2371 were assigned to the intervention arm and 2276 to the control arm. Participants in the intervention arm were assigned to wear a surgical face mask in public spaces (eg, shopping centres, streets, public transport) over a 14 day period (mask wearing at home or work was not mentioned). Participants in the control arm were assigned to not wear a surgical face mask in public places. The primary outcome was self-reported respiratory symptoms consistent with a respiratory infection. Secondary outcomes included self-reported and registered covid-19 infection. Between 10 February 2023 and 27 April 2023, 4647 participants were randomised of whom 4575 (2788 women (60. 9%); mean age 51. 0 (standard deviation 15. 0) years) were included in the intention-to-treat analysis: 2313 (50. 6%) in the intervention arm and 2262 (49. 4%) in the control arm. 163 events (8. 9%) of self-reported symptoms consistent with respiratory infection were reported in the intervention arm and 239 (12. 2%) in the control arm. The marginal odds ratio was 0. 71 (95% confidence interval (CI) 0. 58 to 0. 87; P=0. 001) favouring the face mask intervention. The absolute risk difference was -3. 2% (95% CI -5. 2% to -1. 3%; P

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