BARCELONA, Spain (AP) — The organizers of an indoor music festival in Barcelona to test the effectiveness of same-day coronavirus screening said Wednesday that preliminary results indicate there was zero transmission inside the venue.

The results were released over two weeks since 1,000 music fans volunteered to take part in the experiment. After passing an antigen test on site, around 500 people were randomly selected to enter the concert hall. The other 500 were sent home and used as a control group.

All participants were called back to take a second test eight days later. The results showed zero infections among the 463 concertgoers who complied with the second round of testing, while the control group of 496 people who did not get into the concert had two positive cases.

The concertgoers were obliged to wear masks inside the concert, but dancing and singing were allowed.

The experiment was organized by Barcelona’s The Fight AIDS and Infectious Diseases Foundation along with the Primavera Sound music festival.