1050 people tested positive for COVID-19 after attending a music festival in the Netherlands earlier this month. Utrecht’s regional heath board reported the figures, CNBC points out. The festival in question, Verknipt, is an outdoor event that was held on July 3 and 4 at Recreatieplas Strijkviertel, a park, lake, and recreation area in Utrecht. About 20,000 people attended over both days, and while social distancing measures weren’t enforced, attendees were required to prove through a QR code-based system that they had either been vaccinated against COVID, recently tested negative, or recently recovered from the virus.

“We cannot say that all these people were infected at the festival itself; it could also be possible that they’ve been infected while travelling to the festival or in the evening before going to the festival or having an after-party,” spokesperson for the Utrecht health board Lennart van Trigt said in a statement. “So they’re (the cases) all linked to the festival but we can’t 100% say they were infected at the festival.”

He called the number of cases “quite staggering” and suggested that it could still increase, pointing to how it emphasized problems with the “test for entry” system, which allowed people to use the results of COVID tests taken up to 40 hours before the festival to gain entry. “We’ve found out now that this period is too long,” he said. “We should have had a 24 hour [period], that would be a lot better because in 40 hours people can do a lot of things like visiting friends and going to bars and clubs. So in a period of 24 hours people can do less things and it’s safer.”

He also brought up that people were eligible to attend the festival right after being vaccinated against COVID, instead of at least two weeks later once immunity reaches a higher level. “We were a bit too trigger happy,” he said.

Dutch Prime Minister Mark Rutte and Health Minister Hugo de Jonge said they’d lifted COVID restrictions too early, and made an “error of judgement.” Discos, and nightclubs are now required to close again until August 13, and other restrictions have been put back into place.