SARS-CoV-2 transmission in an indoor mass-gathering live music event. A randomized clinical trial.

Abstract The banning of mass-gathering indoor events to prevent SARS-CoV-2 spread cause an important impact on local economies. We designed a randomized-controlled open-label trial to assess the effectiveness of a comprehensive preventive intervention for a mass-gathering indoor event (a live concert) based on systematic screening of attendees with antigen-detecting rapid diagnostic tests, use of facial mask, and adequate air ventilation. According to a RT-PCR test performed on day 8 after the event, none of the 465 assistants in the experimental arm (i.e., event attendants) became infected by SARS-CoV-2 (observed incidence 0%; Bayesian estimated incidence 0.14%; 95%CI: 0% to 0.61%) versus 2 out of 495 controls (not entering into the event) (0.31%; 95%CI: 0.04% to 0.73%). No significant differences were observed between the estimated incidence in the two study arms. Our study provides evidence on the safety of indoor mass-gathering events conducted during a COVID-19 outbreak under a comprehensive preventive intervention. (ClinicalTrials.gov number, NCT04668625)