Owners of the ski-themed Aspen Valley nightclub in the city of Enschede in eastern Netherlands couldn’t wait to reopen their venue after more than a year of harsh lockdowns brought on by the COVID-19 pandemic. They did everything the Municipal Health Authorities told them to do before opening on June 26: require all customers to present vaccine certificates or negative COVID-19 tests. No face masks or social distancing was required for the revelers.

What they apparently didn’t account for was how desperate the customers were to dance. So far, 165 of the 650 nightclub goers have tested positive for the virus despite the precautions. Now they know that many of those who attended shared screen grabs of Q-codes or negative tests and the bouncers didn’t notice.

Health authorities are asking that everyone who danced at the club that night self isolate until everyone can be tested.

The Netherlands is one of many countries that have eased lock down measures by requiring “test for entry” at all mass gatherings. But since the nightclub fiasco, new infections in the city are up 145 percent, according to the Dutch media.

Party goer Tim Boxen, 20, told a local newspaper that of the 18 friends he went to the club with, nine have so far tested positive. He said he and his friends all have real COVID test results, but few others did. “There was cheating going on everywhere,” he said, describing people sending their negative results to each other’s phones.

In the Netherlands, people are also given vaccination certificates just one day after they complete their last dose, even though immunity doesn’t start right away and in most cases people are not fully immune for two weeks. And when people are required to take a test 48 hours before attending an event, most don’t quarantine to stay COVID-free in the meantime. “Something that does bother me is that customers can do their test 40 hours in advance,” a bartender told the local newspaper. “So someone gets tested on Friday afternoon, goes to football practice, has a beer with friends and then comes to us 33 contacts later.”

The Dutch supersreader party is just the latest example of how things can go terribly wrong when reopening. Nearly 700 students from Madrid who attended an end-of-term party all tested positive for the virus despite having been tested before entering. Those students had contact with nearly 3,000 others upon their return, who all had to quarantine.

Despite by now well-known scientific evidence that mass gatherings of maskless people is the easiest way to spread the disease, and that those who are vaccinated can still transmit it, summer fun seems to be more important for many. The World Health Organization last week noted concern over a surge in cases across Europe, tied to the European Soccer Championships held in 11 countries which have gathered massive crowds of people who, like the Dutch dancers, have also been tested or vaccinated.