Human behaviour: Limiting SARS-CoV-2 transmission in large indoor events

The transmission of SARS-CoV-2 at large indoor events could be limited with effective ventilation and suitable hygiene measures, suggests a paper published in Nature Communications. The research is based on an experimental event held in Germany in August 2020.

When the pandemic began one of the first actions taken by many governments was to ban large events, which has had significant economic impacts.

Stefan Moritz and colleagues investigated the potential transmission of SARS-CoV-2, through aerosols and droplets at an experimental, seated pop concert held in August 2020. The concert was attended by 1,212 participants, who had monitors to record their contacts, under three hygiene scenarios: no restrictions, moderate restrictions (which included checkerboard seating and twice as many entrances as the no restrictions scenario), and strong restrictions (with seating 1.5 metres apart and four times as many entrances as were in place under no restrictions). The authors found that the mean number of contacts per participant was nine people, with the highest number of contacts occurring during entry, interval and exit. They found that under no restrictions contacts of over 5 minutes were created throughout the event, but for moderate and strong restrictions most contacts occurred in the entry phase.

The authors then developed a model of the indoor space and simulated infectious aerosol distribution and the resulting exposure of healthy subjects to SARS-CoV-2. Their model assumed 4,000 concert attendees including 24 who were infectious. They modelled two ventilation scenarios with different air exchange rates and different airflows. They found that under the ventilation scenario with a faster air exchange rate, the mean number of exposed people per infectious person was 3.5 and under the scenario with a slower air exchange rate this increased to 25.5. Implementing hygiene practices reduced the number of people exposed under both ventilation scenarios. Under moderate hygiene restrictions the mean number of exposed visitors per infectious person was 1.9 in the ventilation scenario with faster air exchange and 11.6 in the slower air exchange scenario, with strong restrictions it was 0.7 and 5.3 respectively. The authors then used this information to simulate the impact of a large indoor event on the regional spread of SARS-CoV-2. The authors suggest that with the correct hygiene practices and effective ventilation, large indoor events would have very little effect on the spread of SARS-CoV-2 in the wider community.

The authors note that their results are based on a seated concert and will have limited applicability to other large-scale events, such as standing concerts or football matches.