An interesting article published by Revollo and others in The Lancet Infectious Diseases May 27th 2021 sought to research and answer this question.  

The banning of mass gathering indoor events to prevent SARS-CoV-2 spread has had important effects on local economies.  

Despite growing evidence on the suitability of antigen testing rapid diagnostic tests for mass screening at the event entry, this strategy has never been assessed under controlled conditions.  

This study aimed to assess the effectiveness of a prevention strategy during a live indoor concert.  

The authors designed a randomised controlled open label trial to assess the effectiveness of a comprehensive preventative intervention for mass gathering indoor i.e. live concerts, based on systematic same day screening of attendees with rapid flow lateral flow antigen tests, use of facial masks and adequate air ventilation.  

This event took place in the Sala Apolo Auditorium in Barcelona, Spain.  

Adults aged 18 to 59 years with a negative result in a rapid flow antigen from a nasopharyngeal swab collected immediately before entering the event were randomised one to one and stratified by age and gender to either attend the indoor event for five hours or go home.  

Nasopharyngeal specimens used for the rapid flow screening were analysed by PCR and cell culture.  

Eight days after the event, a nasopharyngeal swab was collected, analysed by lateral flow PCR and transcription mediated amplification.  

The primary outcome was the difference in incidence of PCR SARS-CoV-2 infection at eight days between the control and the intervention group, this was assessed in all participants who were randomly assigned to attend the event and had a valid result for SARS-CoV-2 done at follow up.  

The study involved 1047 people being randomly assigned to either enter the music event, the experimental group, or continue with normal life, the control group.  

Of the 523 randomly assigned to the experimental group 465 were included in the analysis of the primary outcome; 

  • 51 did not enter the event
  • 8 did not take part in the follow up assessment 
  • 524 randomly assigned to the control group
  • 495 were included in the final analysis
  • 29 did not take part in the follow up.  

At baseline 15 that is 3% of the 495 individuals in the control group and 13 that is 3% of 465 in the experimental group, tested positive on TMA despite a negative lateral flow test.  The PCR test was positive in one case in each group and cell viral cultures were negative in all cases.  

Eight days after the event two, less than 1% the individuals in the control group had a positive lateral flow and PCR result whereas no lateral flow nor PCR positive results were found in the experimental group, (those that attended the concert).  

The researchers argue that this is the first randomised clinical trial that assesses the risk of COVID-19 transmission in indoor mass gathering live concerts done under comprehensive safety measures including same day SARS-CoV-2 screening with lateral flow antigen tests, compulsory N95 facemask wearing and optimised air ventilation.  

The participants were encouraged to sing and dance in the concert hall room and no physical distancing was recommended.  

None of the 465 participants became infected compared with two of the 495 in the control arm.  

Other measures that might have contributed to the safety of the event were the N95 mask wearing being mandatory during the event except when drinking (alcoholic beverages were allowed) or smoking.  

The lack of facial mask wearing during indoor activities without physical distancing measures has been pointed out as a high risk scenario for super spreading events.

Other measures that potentially contributed to creating a safe environment included limited movement of participants inside the venue, avoidance of queues in restaurants and entry or exit of the concert, the presence of dispensers of sanitiser gel, and controlled environment conditions.  

Limited air exchange in closed spaces is associated with an increased risk of SARS-CoV-2 transmission.  

Multiple infection events that prompted the banning of mass gatherings have been associated with inadequate ventilation.  

In this study, all air flows and room ventilation were optimised in the indoor rooms and air exchange monitored during the entire event.  

This study provided the first approach to evidence building on the safety of indoor mass gathering events during the COVID-19 outbreak without physical distancing measures and based on a comprehensive preventative intervention including same day screening with lateral flow antigen tests, compulsory facial mask wearing and adequate ventilation.  

The lateral flow antigen screening was effective in identifying infectious individuals compared with PCR and TMA.  

The results regarding biological assessment suggest the baseline screening might allow easing of some of the additional preventative measures, particularly indoor events with pre-assigned seats i.e. theatres, associated with a lower transmission risk. 

The authors argue that their study paves the way to reactivate cultural activities halted during COVID-19 which will have important sociocultural and economic implications.  

The London General Practice, the leading London doctors’ clinic, is proud to be on the government’s approved list for all forms of COVID testing.  This includes rapid antigen tests, same day COVID PCR tests and all tests needed for travel.  

This includes the compulsory day two and day eight tests if required and also the test for release, day five COVID PCR test.

Dr Paul Ettlinger
BM, DRCOG, FRCGP, FRIPH, DOccMed

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