When music fan Noah Zelinsky bought tickets to the Chicago music festival Lollapalooza in May, he thought it might signal something of a return to normalcy after more than a year of isolation. “There’s so much pent up excitement, being the first major thing back,” he says. But a lot can change in two months. “Now, there’s a lot of fear countering that.” As Lollapalooza arrives, along with its potentially hundreds of thousands of attendees, in Grant Park, worrying signs abound: the highly contagious Delta variant of the coronavirus has spread across the U.S., with Chicago’s COVID-19 daily case rate quintuple what it was a month ago , albeit nowhere near the heights of this spring . And recent music festivals, including the Verknipt festival in Utrecht, Netherlands, and Rolling Loud in Miami, have been connected to outbreaks among their attendees and surrounding communities. Whether or not Lollapalooza, which runs from July 29 through Aug. 1, succeeds in holding COVID-19 at...