A trial indoor concert held in Barcelona last month was considered a success after there was almost no sign of Covid-19 infection among 5,000 unvaccinated people who attended.
The show on March 28 was billed as Europe’s biggest indoor rock concert since the start of the pandemic.
It was organised by the Germans Trias i Pujol hospital in Barcelona and a group of Spanish music promoters.
Josep Maria Llibre, a specialist in infectious diseases at the hospital, said there was “no sign that suggests transmission took place during the event” after participants had PCR tests two weeks after the concert.
Attendees wore FPP2 surgical masks at the concert but there was no assigned seating or mandatory social distancing, although capacity at bathrooms was limited to avoid crowding.
Everyone involved underwent mass screening before the event, including antigen tests. Fifteen days later, only six people tested positive for Covid-19.
"We are certain that in four of these six cases, transmission did not take place during the concert," Dr Llibre said.
"With optimised ventilation, antigen tests and the wearing of face masks, we can guarantee a safe space."
Boris Revollo, the virologist involved in designing health protocols at the concert, said he could not rule out that the other two people were infected during the concert but there was a "very high probability" that they were not.
"The measures that we implemented were very safe," he said.
The venue could hold 17,000 people, but the 5,000 ticket holders were not allowed into the stands and were restricted to the dancefloor.
Deputy mayor of Barcelona, Jaume Collboni, said the results of the study showed "it is possible to relax" virus health restrictions and "restart cultural activities".
Trial concert or festivals have been held in several European countries, including in Germany and the Netherlands, as part of efforts to allow crowds at live music events.