CHICAGO (AP) — The hordes of people expected to descend on Chicago’s Grant Park for the Lollapalooza music festival this week will be required to show proof that they’ve been vaccinated for COVID-19 or tested negative for the disease within the last three days.

The four-day festival starts Thursday and is expected to be back at full capacity, with roughly 100,000 daily attendees. After missing last summer because of the coronavirus, it will be easily Chicago’s largest gathering since the pandemic started.

To gain entry, attendees will have to present vaccination cards or a printed copy of a negative COVID-19 test that is no more than 72 hours old. The unvaccinated will also have to wear masks.