CHICAGO (WGN) — Officials for the Lollapalooza music festival announced on Friday that masks will be required of all patrons in any indoor spaces at Grant Park as of Saturday, based on advice from the Chicago Department of Public Health.

This year’s festival officially kicked off Thursday, July 29. At the time, attendees only needed to provide vaccination cards or proof of a negative COVID-19 test for admission each day.

The new mask requirement is now in place for all attendees at indoor spaces, whether vaccinated or unvaccinated. Unvaccinated attendees are also required to “wear a mask throughout your time onsite,” per the festival’s health policy.

The announcement comes as federal, state and local health officials grapple with a rapid rise of COVID-19 cases, many of which can be attributed to the more contagious delta variant. Illinois alone has reported over 11,600 new COVID-19 cases over the last 7 days.

Organizers of this year’s festival, meanwhile, have claimed that 90% of Thursday’s attendees provided proof of vaccination, while only around 600 people were turned away for not providing vaccine cards or negative test results.

Lollapalooza 2021 will continue through Sunday, Aug. 1, with performances from Post Malone and Journey scheduled for Saturday night, and Foo Fighters and DaBaby on Sunday, among others.