Despite being billed as a COVID-19 safe event, preventing entry of anyone who is neither fully vaccinated nor can provide a negative test, now some 10,000 people have contracted the virus.

“We cannot say that all these people were infected at the festival itself,” said Lennart van Trigt, a spokesman for the Utrecht health board. “It could also be possible that they’ve been infected while traveling to the festival or in the evening before going to the festival or having an after-party.” However, CNBC reports that the event is at the center of the outbreak, as confirmed by Utrecht’s regional health board.

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It is also possible that the one in 20 concert-goers who have been affected could have contracted the virus shortly after receiving negative test results. They were allowed to get tested up to 40 hours prior to the event which was “too long,” according to van Trigt. “In 40 hours people can do a lot of things like visiting friends and going to bars and clubs,” van Trigt added. The window has since been minimized to 24 hours.

Van Tricht admits the entire city has been “a bit too trigger happy.”

Until last week, the Dutch health department was distributing Covid passes immediately upon vaccination, without waiting for the roughly two-week delay before protection builds. The Dutch prime minister and health minister have since apologized for lifting restrictions too early.