Last year’s edition of Trans-Siberian Orchestra’s annual holiday tour was an outing unlike any other for everyone involved in bringing the visually spectacular concerts to audiences across the United States.

On the one hand, coming off of 2020, a year in which the TSO Christmas tour could not happen because of the COVID pandemic, there was a special excitement and appreciation for being back in arenas and performing the concerts.

“Missing 2020 certainly made us realize how fortunate we are to do what we do,” said Jeff Plate, who is the drummer for TSO’s eastern U.S. touring unit.

But it was also the most challenging outing in TSO’s history, thanks to the lingering issues with COVID.

“It was riddled with anxiety, to say the least, because every morning you’d wake up and it’s like ‘OK, is somebody sick? Did somebody test positive? What are we going to do? Is the crew there? Are the folks in the audience OK?’,” said Al Pitrelli, who is musical director for the western U.S. unit of TSO. “So it was definitely the most stressful tour we’ve ever been on.”

It’s not as though TSO didn’t take precautions for COVID or have contingencies in place in case any of the performers came down with the virus. As Pitrelli noted, the job is to deliver the memorable concert spectacle fans have come to expect and make sure any issues aren’t apparent to audiences.

“The audience just wants their show. Whatever hoops we’ve got to jump through to make that happen, that’s what we’re going to do,” he said.

Pitrelli and Plate, obviously, are hoping this year’s TSO tour will be more like the pre-pandemic outings, when words like daily testing, social distancing and masking weren’t associated with rock shows.

Over its first two decades, TSO’s shows have become easily the biggest and most elaborate of the holiday tours. It was all the vision of the group’s founder, Paul O’Neill, who sadly passed away in 2017.

O’Neill’s idea was TSO would combine a rock band with an orchestra playing concept albums/rock operas with cohesive story lines. Instead of building an image around a singer, guitarist or conductor, the ensemble would use multiple singers and a range of instrumentalists, who would remain largely anonymous to listeners.

Atlantic Records got on board with O’Neill’s vision and signed TSO. The label has been rewarded, as the trilogy of lyrically-themed Christmas albums all became hits and continue to rack up Top 10 sales among holiday albums each Christmas season.

The first release was 1996’s “Christmas Eve and Other Stories.” Spurred by the hit single “Christmas Eve Sarajevo 12/24,” it has sold  3 million copies and set the stage for the other two holiday rock operas that make up TSO’s Christmas trilogy — “The Christmas Attic” (1998) and “The Lost Christmas Eve” (2004) – which have each topped 2 million copies sold. In all, the group’s CDs and DVDs have sold more than 12 million copies and generated 180 million streams in 2021 alone.

The group’s annual Christmas trek is easily the most popular holiday tour going. Since its debut in 1999, the holiday tours have played to about 18 million fans and grossed $725 million.

The entire TSO organization, of course, misses O’Neill. But Plate said the good thing is O’Neill and his family surrounded themselves with a stellar team that knows every part of the operation.

“Paul told us many, many, many times this thing is going to outlive us all and it’s going to last from generation to generation,” Plate said. “Thinking for a moment that it would be without him was not in any of our thoughts. When it happened, it’s like ‘Well guys, we know what to do. We know what the job is.’ … We’re doing it for, not just for the audience, but for Paul and his family, and it means a lot to us.”

This year’s show finds TSO performing “The Ghosts of Christmas Eve,” which is a 2001 DVD that combined the most popular songs from “Christmas Eve and Other Stories” and “The Christmas Attic.”

“The Ghosts of Christmas Eve” will take up most of the first half of the show, followed by a second part that draws on selections from across the TSO catalog. Because many of the most popular songs will be performed as part of “The Ghosts of Christmas Eve,” Pitrelli, Plate and the musicians had room for some songs this year that haven’t often been performed on past tours.

“We have a lot of conversations. Everybody will throw their ideas in,” Pitrelli said about crafting the set list. “We have such a large catalog of material to draw from … all of a sudden a song will pop up, like wow, I haven’t heard that song in so long. Let’s try that this year.”

One thing Pitrelli and Plate couldn’t speak to is how this year’s visual effects and stage set will be bigger and different from last year. This interview was conducted in October, a short time before they joined the band for production rehearsals.

“You look up, and I always feel like a 15 year old walking into that arena for the first time,” Pitrelli said. “It really turns you back into a teenager. But this time I’m not getting chased out by security or the police.”

TSO plays in St. Louis Friday, Dec. 10 at the Enterprise Center.