Comic-Con International, which considers itself the oldest pop-culture convention in the world, is returning to San Diego for its first major in-person event since before the coronavirus pandemic began, and masks will be mandatory.
The gathering starts Thursday and runs through Sunday at the San Diego Convention Center, just as cases of the coronavirus are soaring in the county and in other parts of the United States. In recent months, however, mask mandates have been dropped in most states and cities.
Organizers said they were expecting more than 135,000 people at the event. In addition to wearing masks, attendees must also provide proof of vaccination, or of a negative coronavirus test taken within the previous 72 hours, according to the Comic-Con International website.
In San Diego, the Centers for Disease Control and Prevention raised the community risk level from “medium” to “high” on Thursday. The risk levels, according to the C.D.C., are based on the number of occupied hospital beds and admissions and the total number of new coronavirus cases in a region.
Under a “high” designation, the C.D.C. recommends that people wear masks in indoor public spaces. San Diego County “strongly recommends,” yet does not mandate, them.
But the organizers of Comic-Con said that in planning the event several months ago, they had preferred to err on the side of caution, given the highly unpredictable course of the pandemic.
“We’ve been very pleasantly surprised by the feedback we’ve gotten, which has been overwhelmingly positive,” said David Glanzer, a spokesman for Comic-Con International. He added that precautions like wearing a mask were a “small price to pay” to get together again at shows.
As of Sunday, an average of 2,100 cases per day were being reported in San Diego County, a 18 percent increase from the average two weeks earlier, according to data from The New York Times. Hospitalizations and deaths have also risen.
North of San Diego, in Los Angeles County, the community risk level was also raised to “high” on Thursday. Officials have warned that if the level remains at “high” for two consecutive weeks, they will bring back an indoor mask mandate.
Federal officials have also warned that as the highly transmissible Omicron subvariant known as BA.5 fuels a new wave of infections, reinfections and hospitalizations, Americans must do more to protect themselves against the coronavirus, including wearing masks.
Before the pandemic, Comic-Con International annually drew tens of thousands of fans of fantasy comics, films and video games to San Diego. But in 2020, organizers made the “emotional” decision to cancel the event, Mr. Glanzer said.
It was moved online, and participants were able to watch recorded panels on YouTube. Since then, the organization has held two smaller in-person events, the Comic-Con Special Edition, in November in San Diego, and WonderCon, in April in Anaheim, Calif.
Both events also required that attendees wear masks.
The San Diego Convention Center, where the event is being held, reopened in August, and since then, it has held more than 90 events. Masks were required at some of those and recommended at others, or attendees were required to provide proof of vaccination or a negative coronavirus test, according to Maren Dougherty, a spokeswoman for the center.
Comic-Con, she added, is by far the largest event the center will hold since its reopening. In 2019, the event brought about $150 million into the local economy, Ms. Dougherty said. After several years without large events, she said, those attending events at the center have been largely respectful of protocols.
Plus, “masking has always been part of Comic-Con,” she added. “People have fun with that.”