Preventing SARS-CoV-2 transmission at large indoor events

In light of the growing evidence of the increasing risk of transmission from droplets of indoor air, the unprecedented coronavirus pandemic of 2019 (COVID-19), led to the world-wide prohibition of major indoor gatherings.

The French government banned gatherings with a capacity of 5000 or more people in February 2020 and prohibited all gatherings of mass from March 2020. At that time it was clear that mass gatherings were causing the spread of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections at the national and community levels.

There was accumulating evidence on the transmission risk from asymptomatic carriers and aerosols in indoor gatherings. Nightclubs and indoor concert venues were deemed’super-preader events’ because of their insufficient ventilation and lack of mask wearing standards. People who worked in the events industry, particularly the young ones, suffered a lot of socio-economic and psychological effects from the ban on gatherings of mass size.

After being closed for more than 15 months, and with the availability vaccines against COVID-19 now available authorities are contemplating opening venues for live performances or nightclubs.

Study Prevention of transmission of SARS-CoV-2 during an extensive, live, indoor gathering (SPRING) as a non-inferiority randomised controlled trial. Image Credit: BearFotos/Shutterstock

SPRING (Study on Prevention of SARS-CoV-2 transmission at large indoor gatherings) trial examined the hypothesis of a systematic screening for SARS-CoV-2 during the three days preceding the event as well as the use of medical masks by participants to stop transmission of the virus in indoor settings. It is the first noninferiority open label, controlled, randomized trial.

Study design

Researchers working on the SPRING trial screened the audience of a concert that was live that took place at the Accor Arena on May 29, 2021 in Paris, France. The participants who were screened, all aged between 18 and 45 were recruited via an official website. They did not have COVID-19-related symptoms or comorbidities or recent contact with a COVID-19 affected person. Also, they tested positive in a rapid antigen test (RAT) performed within three days prior to the concert.

Between May 11 and May 25 the period, there were 18,845 registered on the site. However only 10,953 users were able to sign up for an on-site visit. The researchers only screened 6,968 people from these. The computer generated allocation sequence used permuted blocks of sizes three six, nine, and three. Researchers randomly assigned the enrolled participants to the experimental (attendees) or control (non-attendees), in a 2:1 proportion without stratification. There were 6,678 people enrolled. 4,451 were assigned as attendees to the experimental group and 2,227 to non-attendees to the control group.

Results

The follow-up requirements could be met by 88 percent of participants and 87% of non-attendees. RT-PCR was positive for three non-attendees and eight attendees on day 7, indicating they met the non-inferiority criterion for the primary endpoint. The analysis yielded the absolute positivity-rate differences of 95% CI between the two groups, and an incidence rate ratio (IRR) of 1*33.

Of the 14 participants who had positive saliva on day 0, eight showed negative RT-PCR in their saliva on day 7, suggesting they were in the final stages of infection. Hospitalization was not required for any participant who had RTPCR-positive saliva. After the event, four attendees and two non-attendees reported mild COVID-19-suggestive symptoms.

The computer algorithm was employed by researchers to identify 33,349 faces in the event. The faces were classified as having inadequate adequate, inadequate, or with no masks by the researchers. The overall median for mask-wearing compliance was 91.4 percent; 90.0% compliance on the arena floor and 97.4% in the lobby and the staircases, which remained stable over the 4 hours.

Limitations

The study has two major limitations. First, the participants were aware that they were under surveillance, which may have altered their natural behavior, limiting the ability to apply the findings to a real-life scenario. Also, the rate of fully vaccinated participants was 7.2%, and the greater the immunization rate the lower the risk of SARS-CoV-2 transmission during the gathering.

The other issue was that the SARS-CoV-2 infection were declining in France in the months between May 2021 and May 2021. the majority of the infections were caused by the SARS-CoV-2 alpha variant which is less transmissible than the delta variant. The prevention measures of the trial could have been extremely efficient in this situation.

Conclusion

To conclude, the findings of the SPRING trial proved that participating in an indoor live event isn’t associated with an increased risk of contracting SARS-CoV-2, provided preventive interventions are in place during these events.

This trial also demonstrates that large-scale gatherings, such as live concerts, can be resumed despite the continued transmission of highly transmissible SARS CoV-2 variants.