Development of a COVID-19 risk-assessment model for participants at an outdoor music festival: Evaluation of the validity and control measure effectiveness

We developed an environmental exposure model to estimate the Coronavirus Disease 2019 (COVID-19) risk among participants at an outdoor music festival and validated the model using a real cluster outbreak case. Furthermore, we evaluated the extent to which the risk could be reduced by additional infection control measures such as negative proofs of antigen tests on the day of the event, wearing masks, disinfection of environmental surfaces, and vaccination. The total number of already- and newly-infected individuals who participated in the event according to the new model was 47.0 (95% uncertainty interval: 12.5-185.5), which is in good agreement with the reported value (45). Among the additional control measures, vaccination, mask-wearing, and disinfection of surfaces were determined to be effective. Based on the combination of all measures, a 94% risk reduction could be achieved. In addition to setting a benchmark for an acceptable number of newly-infected individuals at the time of an event, the application of this model will enable us to determine whether it is necessary to implement additional measures, limit the number of participants, or refrain from holding an event.