COVID risks higher from small indoor events than large outdoor ones: research

Outdoor events are safer than indoor events in regards to potential COVID-19 transmission, according to a newly released comparative study of two hypothetical events in Austin, Texas.

A study from the University of Texas and the city of Austin considered the COVID-19 transmission risks at two events: a business conference with 3,000 attendees during a pandemic surge and an outdoor festival with 50,000 attendees in a low transmission period.

Despite the attendance at the hypothetical outdoor festival being more than 10 times higher than at the indoor business conference, the study’s authors estimated that the festival would result in the infection of only twice as many people in the community during and after the event.

To calculate the COVID-19 risks from the two events, they considered multiple factors: the structure of the event, including its size, duration, density and venue; the state of the pandemic, including the local prevalence of the virus and the epidemiological properties of current variants; any risk-reduction measures introduced by event organizers; and local demographics.

Using that information, the study’s authors said they first estimated the number of attendees who would arrive infected at the hypothetical events. To do this, they said they used the COVID-19 school risk dashboard to estimate the incidence rates of COVID-19 in every U.S. county and assumed that an attendee arriving infected correlated directly to the incidence rate of infection in their home county.

They said they then estimated the number of attendees who would be infected at the event and finally the total number of infections in Austin that would stem from the event over a four-week period.

The study’s authors said that the risks of transmission from an event can be significantly reduced by requiring proof of vaccination, a negative COVID-19 test just prior to the event and/or the wearing of face masks during the event.

The results of the study also showed that limiting the number of attendees, physically spacing out activities and selecting outdoor and well-ventilated sites can significantly mitigate risks, the authors said.

However, the authors cautioned that they made “a number of critical assumptions that may not hold for all events, especially as SARS-CoV-2 and our arsenal of medical countermeasures continues to evolve.”