Covid-19: Indoor Events Possible Without Risk of Viral Transmission

A randomized study published in Lancet Infectious Diseases suggested ways that people can attend live music and other cultural events without increasing their risk of contracting Covid-19.

“To our knowledge, this is the first randomized clinical trial that assesses the risk of COVID-19 transmission in an indoor mass-gathering live concert done under comprehensive safety measures, including same-day SARS-CoV-2 screening with Ag-RDTs, compulsory N95 face mask wearing, and optimized air ventilation,” Josep Llibre, MD, of the Germans Trias i Pujol University Hospital, Spain, and colleagues wrote. “Participants were encouraged to sing and dance in the concert hall room, and no physical distancing was recommended.” No one attending the concert developed Covid-19 and only two people in the control group were diagnosed with Covid-19 within eight days of the event.

Llibre noted in a press statement, “Our study provides early evidence that indoor music events can take place without raising the risk of SARS-CoV-2 transmission when comprehensive safety measures are in place, but it is important that our findings are considered in light of the situation in Spain at the time—when cases were not high and many restrictions were in place. As a result, our study does not necessarily mean that all mass events are safe.”

In an accompanying editorial, Rossana W. Peeling, PhD, and David L. Heymann, MD, from the Clinical Research Department and the Department of Infectious Disease Epidemiology, respectively, at the London School of Hygiene and Tropical Medicine, note that Llibre et al’s study underscores the importance of well-designed studies, especially in light of innovative use of antigen rapid diagnostic tests (ag-RDTs). Moreover, they noted that the study begs certain questions:

• “[W]ould triple-layered masks have been sufficient?
• “How does rapid antigen testing at entry compare with molecular screening within 72 hours of entry?
• “Does screening create bottlenecks with an increased risk of transmission among those not yet tested?
• “Which study design would be required when attendees are not all from the same community but attending international events such as the Olympic and Paralympic Games?
• “And the question of concern for all is whether existing RDTs are able to detect Covid-19 variants of concern and the role of vaccination.”

Barcelona was the site of the indoor concert event and participants in the study were subscribers to news related to live music events, from which they were recruited. Those eligible for the study were adults age 18-59 with a negative ag-RDT obtained from a nasopharyngeal swab that was collected the morning of the event. Exclusion criteria included those who had a known Covid-19 diagnosis within 14 days before the event and those with comorbidities such as hypertension, diabetes, or any type of cancer.

Those who were eligible for the study were randomized to either the experimental group (n=465) who were allowed to attend the concert or to the control group (n=495) who could not enter the event but were told to “return to normal life.”

Concert attendees had their temperatures taken, were given N95 masks and told it was mandatory that they wear the masks throughout the event. However, physical distancing was not required in the concert hall, which had a 900-seat capacity.

But the event was not without restrictions: there was an outdoor smoking area with a 20-person limit and strict crowd control and social distancing. Drinks were served at which point the attendees could remove masks but only while drinking. The bar area was in a separate area with a 1,600-person capacity. Movement within the venue was controlled and some areas were closed off. The venue was also well-ventilated.

Participants were also asked to download two phone apps to facilitate contact tracing. Participants in both the experimental and the control groups were visited eight days after the concert and tested for Covid-19.

Of note, the concert lasted five hours and attendees were inside the concert hall on average just under three hours.

“None of the 465 participants in the experimental group became infected by SARS-CoV-2 (observed incidence 0%; estimated incidence 0.14%, 95% CI 0-0.61) versus two of 495 controls (0.31%, 0.04-0.73), as assessed by a positive RT-PCR test on day eight. The two participants in the control group with SARS-CoV-2 infection had positive Ag-RDT and RT-PCR (Ct values 26.3 and 28.3) results in the follow-up assessment on day eight,” Llibre and colleagues wrote.

The study authors found that one of the individuals who tested positive had been diagnosed four days after randomization, and both of them had mild disease.

“The negative predictive value of the Ag-RDT screening in this cohort of asymptomatic individuals was 99.9% (95% CI 99.5-100) for a positive RT-PCR, and 99.8% (99.3-100) for a positive viral culture,” the study authors wrote. “The air concentration of CO2 did not exceed the recommended threshold of 800 ppm at any time point during the event. The number of complete air exchanges per hour in the two rooms ranged from 11 to 13.”

The participants who attended the event reported rated their experience 8.63 out of a 10-point scale assessing their satisfaction and enjoyment.

“Most event attendees felt they could behave normally and non-constrained despite the safety measures (median score 8.08, IQR 5–10),” the study authors reported. “They expressed their willingness to attend another activity with the same safety protocol (median score 9.29, IQR 9–10). There were neither disturbances nor interventions of security personnel aside from reminders of wearing the face mask during the event.”

In the press statement, Llibre also noted that uptake of vaccinations as well as “changes in local incidence and the emergence of SARS-CoV-2 variants with higher transmissibility could all impact the interventions we tested, so we need more studied including larger numbers of people that explore different scenarios and policies that take into consideration the local context.”

The study authors acknowledge some limitations of their study—the attendees may have modified their behavior because they knew they were being observed and the planned number of study participants was cut in half because of public health restrictions.

1. Indoor mass-gatherings, if done under comprehensive safety measures—including same-day SARS-CoV-2 screening with Ag-RDTs, compulsory N95 face mask wearing, and optimised air ventilation—are possible with no viral transmission.

2. Be aware that this study was conducted when cases of Covid-19 in Spain were not high and many restrictions were in place and therefore does not necessarily mean that all mass events are safe.

Candace Hoffmann, Managing Editor, BreakingMED™

Cat ID: 190

Topic ID: 79,190,730,933,190,926,192,927,151,928,925,934