About 52,000 people attended a huge pop concert at Copenhagen’s Parken stadium in Denmark.
The concert was organised a day after Denmark abolished coronavirus restrictions.
The event was Europe’s first concert hosting more than 50,000 people since the pandemic began.
As of September 15, Danish health authorities had recorded 353,451 cases and 2,617 coronavirus deaths.
While vaccines are effective in protecting people against severe disease and death, they cannot stop the infection.
The more contagious Delta variant, for instance, has broken through the vaccines in several countries.
People might still get sick, Simonsen said, but in most cases, illness will be milder with fewer hospitalisations and deaths.
But as many are step back into their pre-pandemic routines, some have reservations.
The event took place only a month after the World Health Organization (WHO) expected that another 236,000 people could die from COVID-19 in Europe by December 1.
The health organisation raised the alarm over the rising infections and stagnating vaccine rates on the continent.
“Last week, there was an 11 percent increase in the number of deaths in the region – one reliable projection is expecting 236,000 deaths in Europe, by December 1,” WHO Europe director Hans Kluge said.
Kluge said the Delta variant was partly to blame, along with an “exaggerated easing” of restrictions and measures and a surge in summer travel.
“In the past six weeks, it has fallen by 14 percent, influenced by a lack of access to vaccines in some countries and a lack of vaccine acceptance in others,” Kluge said, urging countries to “increase production, share doses, and improve access”.
“Vaccine scepticism and science denial is holding us back from stabilising this crisis. It serves no purpose, and is good for no one.”
The warning comes as the WHO and UNICEF urged European countries to make teachers a priority group for vaccination.