The gathering—in this case a large, annual festival tied to a number of name-brand corporate sponsors—is (for now) scheduled to be held in a sunny resort town after Labor Day. Going into the summer, its planners were confident they had a workable formula. They would reduce capacity, hold socially distanced sessions outdoors, provide on-site testing for staff and guests who were not fully vaccinated, and work with local authorities to make sure other health and safety guidelines were followed.

“I was so optimistic that everyone would be vaccinated and we could control the situation at least at the venue,” said the planner, who asked to have her name withheld to avoid telegraphing behind-the-scenes deliberations ahead of official communications to attendees. “We spent six months putting together a 30-page playbook, and then a few weeks ago we tossed it out and started from scratch.”

What prompted all this, of course, was the Delta variant, which is quickly driving cases of COVID-19 back up toward peak levels, with hospitalizations and even deaths rising across the country—most especially in some of the traditional hubs of the business conference circuit, such as Miami, Orlando, Las Vegas, Austin, and New Orleans. 

Already, some major events are being postponed: September’s New York International Auto Show at the Javits Center has been canceled, and Jazz Fest in New Orleans followed suit. 

Now, marketers, trade associations, event producers, and publicists are engaged in a scrum of cost-benefit analysis, straining to figure out if it makes more sense to move forward, cut their losses, or try to find some elusive middle ground. Fielding questions from sponsors and attendees alike, organizers must make tough calls in concert with venue managers, convention bureaus, unions, public health officials, and policymakers—all of whom face competing pressures of their own. 

At stake: the future of a multibillion-dollar industry still staggering from the very first wave of lockdowns last year.

Depending on the event and its purpose, the calculation of whether or not the show must go on can be very different. Cautious corporate clients have largely scrapped plans for internal events like sales meetings, offsites, and a novel group of welcome receptions for new employees who have never been to the office before. These decisions tend to track amended or curtailed return-to-work policies.

“We were getting inquiries about catering corporate events in September when things were expected to get back to normal, though people asked us for budgets ranging from 200 to 600 people; everyone was a little unsure of how big they were going to go,” says Ryan Corvaia, the founder and CEO of Dish Food & Events, a New York City caterer. “Those inquiries have all stopped.”

Meanwhile, many events are going virtual. Mark Testa, the founder and creative director of Mark Stephen Experiential Agency in New York, says just this week a client who planned to host an event in a southern city decided to move from a live event with a virtual component to an all-virtual event. “They decided a live event just wasn’t worth the aggravation,” he says. 

Like Testa’s client, many marketers who previously believed in the unique power of a live event to dazzle customers have come to discover that virtual events offer plenty of benefits. They can often be produced more cheaply and at a higher margin, and reach a larger audience. “When this all started last year, we shifted as an agency to all-virtual as a matter of survival,” Testa says. “Lots of our clients didn’t like it necessarily, and they didn’t expect much from it. But as time went by, the numbers of people who tuned in were surprisingly good, and we found we could reach customers all over the world. It was kind of cool to see people from Dubai or Nigeria tune in to a virtual event.”

There’s also the question of PR and whether hosting a large event right now is at best tone deaf and, at worst, a reckless reputational risk. Take the notoriously conservative marketers who are key stakeholders in the International Auto Show, for example. The risk of being tied to an outbreak in New York City—at the Javits Center, a venue that served as a mass-vaccination site only a short time ago, no less—likely outweighed whatever positive buzz the automakers could hope to generate for the latest concept vehicle. (What’s more, the car companies and their dealers are already scrambling to keep up with demand—they hardly need to stoke consumer interest this very minute.)

Of course, many organizations—from trade groups to nonprofits to training companies—view events as a fundamental component of their revenue model. For these companies, requiring proof of vaccination along with testing on-site and plenty of hand sanitizer to go around seemed to offer a path forward. But each of these steps comes with added cost, complicating the economics of hosting the event in the first place. 

“If you’re careful, you can manage the budget for small events where everyone is vaccinated or you hire a nurse to test people every day, but for larger events like the auto show, imagine having to do that for the Javits Center,” says Susan Martin, who runs SMARTproductions, a business that has recently overseen events for corporate clients in New Orleans and New York City. “You probably couldn’t overcome that added cost.”

Moreover, efforts to limit exposure, however thorough (and costly), are bound to come up short. Even if you ensure that every attendee, cater-waiter, and lanyard greeter is vaccinated, events by their nature bring all sorts of people together. Planners can only control so much, and at some point it is inevitable that someone on-site will interact with someone outside the bubble, be it the teamster who delivers all the stage and tech equipment, or the police officer providing added crowd control and security, or the shuttle driver who ferries attendees to and from their hotels. 

Faced with uncertain and perhaps unfavorable odds, events marketers are huddling to find out what their peers plan to do, and carefully scrutinizing the fine print. Should they release venues? Speakers? Hotel blocs? Unlike 2020, they likely have options. “Today, there’s not a contract that goes out the door without COVID clauses or pandemic clauses,” says Martin.

For a time earlier this summer, when the rate of new COVID cases remained low, event planners felt as if they had a handle on how to move forward. “With more states eliminating or easing restrictions on large gatherings, the exhibition industry is finally close to the end of the pandemic tunnel,” said Cathy Breden, CEO of the Center for Exhibition Industry Research, in June.

The reprieve turned out to be momentary. “In June and July we thought we were doing the smart thing by waiting until the fall and using the time to plan,” says the woman who is working on the large event planned for next month. “But now we look back and realize that was a really good window.”

More finance coverage from Fortune:

• What are stablecoins? Your guide to the fast-rising alternative to Bitcoin and Ethereum
• Adidas gives Reebok the boot. Will this go down as one of the worst sportswear acquisitions ever?
• As climate worries spike, green bonds are having a moment. Should you invest?
• The daunting challenge ahead for Disney CEO Bob Chapek
• Crypto platform offers $500,000 “bug bounty” to hacker for returning stolen assets