ABSTRACT
Background: Mass indoor gatherings were banned in early 2020 to prevent SARS-CoV-2 spread. We aimed to assess, under controlled conditions, whether systematic antigen-screening within 3 days, medical mask-wearing and optimized ventilation could prevent SARS-CoV-2 spread during a large, indoor gathering without physical distancing.Methods: The non-inferiority, prospective, open-label, randomized (2:1)-controlled SPRING trial was conducted on May 29, 2021 in Paris, France. Participants, 18–45 years old, had no comorbidities, COVID-19 symptoms and recent case contact, and a negative rapid antigen diagnostic test within 3 days before the concert. Participants were randomly allocated to the experimental arm (attendees) or to the control arm (non-attendees). The primary outcome measure was the number of SARS-CoV-2–positive RT-PCR on self-collected saliva 7 days (D7) post-gathering. An artificial intelligence tool analyzing anonymised, continuous video-capture data evaluated participants’ mask-wearing compliance. This trial is registered with ClinicalTrials.gov, NCT04872075.Findings: Among 6678 randomized participants (median age 28 years; 59% women), 88% of each group complied with follow-up requirements. The D7 RT-PCR was positive for eight of the 3917 attendees (observed incidence, 0.20%; 95% Confidence Interval [CI], 0.09 to 0.40) and 3 of the 1,947 non-attendees (0.15%; 0.03 to 0.45) (absolute difference, 95%CI, –0.26% to +0.28%), findings that met the non-inferiority criterion (margin <0.35%) for the primary endpoint. Global facemask-wearing compliance (i.e., covering nose and mouth) was estimated at 91.4% (95%CI, 87.7 to 95.4).Interpretation: Participation in a large, indoor, live gathering without physical distancing was not associated with increased SARS-CoV-2–transmission risk, provided a comprehensive preventive intervention was implemented.Trial Registration: This study was registered on ClinicalTrials.gov (NCT04872075).Funding: French Ministry of HealthDeclaration of Interest: All authors declare no competing interestsEthical Approval: The trial protocol was approved by the Scientific Ethics Committee of the Sud-Ouest and Outremer Regions of France and the French Data-Protection Agency