Airlines warned Thursday of another pandemic-driven hit to profits in the months ahead, as the Delta variant interrupts a rebound in air travel.

Major carriers said new travel bookings have slowed in recent weeks and cancellations have increased, tempering airlines’ outlook after less than two months earlier some had projected the recovery would continue to strengthen.

“The crystal balls have been a little bit foggy to say the least, as we’ve gone through this crisis,” Andrew Nocella, chief commercial officer for United Airlines Holdings Inc., said at an investor conference Thursday.

As recently as late July, airlines looked to be on track for a rapid rebound from the crisis that brought air travel to a standstill when Covid-19 hit the U.S. in early 2020. Travelers flooded back to airports over the summer, and several carriers anticipated profits in the third quarter. While the Delta variant had emerged as a concern, airline executives said they were prepared to navigate an uneven recovery but hadn’t yet seen much impact.

That changed last month. A pickup in business travel that took root over the summer has stalled, airline executives said Thursday. Airlines had been counting on offices to reopen, bringing business travelers back out this fall when summer vacation traffic typically slows down. But many large companies are now delaying returns to the workplace, in some cases through the rest of the year.