Study Shows How to Safely Hold an Indoor Mass Gathering

There was no COVID-19 transmission following an indoor music event with appropriate public health precautions, Spanish researchers found in a randomized trial.

When the use of masks, adequate air circulation, and rapid testing were all employed, 0% of concert attendees tested positive for COVID-19 at 8 days after the concert compared to less than 1% of people who did not attend (control group), reported Josep Llibre, MD, PhD, and colleagues from University Hospital Germans Trias i Pujol in Badalona, Spain.

Interestingly, 3% of participants in the control group tested positive and 3% of the concert attendee group tested positive before the concert using a transcription-mediated amplification (TMA) test, but tested negative via rapid antigen testing, the authors wrote in the Lancet Infectious Diseases.

“These results confirm that with the implementation of these measures, these indoor events are not super spreading events, as they had been previously classified. In addition, the results do not support any increased risk of SARS-CoV-2 transmission during the event,” Llibre told MedPage Today.

While this study made news when the authors shared their findings via press release, this was the first time the results were written up in a peer-reviewed journal.

This represents the first randomized trial to evaluate the safety of indoor mass-gatherings for a live music concert during the COVID-19 era using testing to detect viral transmission, the authors said. The findings offer hope for the possibility of mass-cultural and music events to safely return to societies by using preventative measures.

The gold standard for COVID-19 testing has been RT-PCR, with its high detection sensitivity, but it has a long turnaround time. However, with a low-cost and short turnaround time, rapid antigen tests have been useful in same-day event point-of-care screening, despite their lower sensitivity.

TMA testing also offers rapid turnaround time with high sensitivity, and can test for DNA/RNA infections and has shown comparable performance to RT-PCR testing.

On Dec. 12, 2020, this experiment took place: 960 eligible adults in Spain, ages 18 to 59, were randomly assigned to two groups. One group attended the 5-hour-long indoor concert and one group was sent home. There were 465 participants who attended the concert and 495 participants who did not attend.

All participants were screened via nasopharyngeal swabs administered 12 hours before participants either entered the concert or were sent home. The swabs were tested by a rapid antigen test and further analyzed by cell culture and RT-PCR. Results of rapid antigen testing were visible by an app within 15 minutes of swabbing for eligibility.

Patients were excluded if they tested positive for COVID-19 within the last 2 weeks prior to the study, lived with the elderly or immunocompromised, or had significant pre-existing conditions (cancer, hypertension, diabetes). A negative rapid antigen test result was required for inclusion.

At the concert, temperature screening was performed and participants were given N95 masks to wear. Social distancing was not enforced and concert attendees were permitted to sing and dance, and all access doors remained open for enhanced ventilation.

Hand sanitizers were available and security personnel enforced protocols. Room temperature was about 68°F. There were 58 staff members with a few artists at the venue with the participants, all of whom were tested via rapid antigen testing.

Follow-up was done 8 days after the concert, where participants were swabbed and tested again. Patients underwent contact tracing and submitted health questionnaires before and after the event.

The primary outcome evaluated the COVID-19 transmission risk at the mass gathering, with the incidence difference of RT-PCR-confirmed COVID-19 infection in participants at 8 days between the two groups as the primary efficacy endpoint.

Two members of the control group participants tested positive for COVID-19 at 8 days after the concert (estimated incidence 0.31%, 95% CI 0.04%-0.73%), both with mild clinical disease. However, in the experimental group of those who attended the concert, 0% of participants tested positive (estimated incidence 0.14%, 95% CI 0%-0.61%). Bayesian estimates for the incidence between groups was -0.15% (95% CI -0.72% to 0.44%).

“The situation in the [U.S.] is now much better with rates of complete vaccination in the general population greater than 50% and counting,” Llibre told MedPage Today. “In addition, outdoor mass-gathering events have a significantly lower risk.”

Llibre said further studies are considering whether face masks could be removed if event access is restricted to completely vaccinated individuals or those with a negative test.

The study’s limitations include that it was conducted in Spain, where participants share common demographics, as well as its small size. It is also possible participants changed their usual behavior while being studied, creating a Hawthorne effect. In addition, TMA testing has a high sensitivity using a low detection threshold, so it could generate false positives, the authors said.

Authors cited the need for future studies to further evaluate the safety of mass indoor gatherings, and the need for additional testing on a larger scale. Llibre told MedPage Today that the U.K. is conducting up to 15 pilot studies based on these results, and The Netherlands has also started a program of pilot concerts.