Uncertainty over the spread of the COVID-19 Omicron variant continues to impact the return to school, with 18 bus routes cancelled on Wednesday in the London area, leaving many parents in a lurch.

While local operators have not explained the reason for the recent cancellations, a representative said parents should have a contingency plan.

"All parents should have a backup plan in place ... all of the operators have to have a complement of spare drivers readily available, but who's to say that those backups will not get sick as well," said Nancy Daigneault, executive director of School Bus Ontario, which represents most of the school bus operators in the London region.

The weather was not a factor in the bus cancellations Wednesday that impacted service to schools in the ​​Thames Valley District School Board and the London District Catholic School Board.

Daigneault said it's too early to know precisely why there were so many cancellations, but said there have been driver concerns around the Omicron variant.

"[It's] definitely been expressed from some of the drivers that they are worried about the fact that [Omicron is] a lot more contagious than the earlier variants," she said. "Absolutely, they're calling in and saying that they are concerned about that."

School Bus Ontario is "anticipating" that some drivers will fall ill with Omicron because of its contagiousness.

Daigneault explained there's a "severe driver shortage" that predates the pandemic, going as far back as 10 years. She said that COVID-19 has made it worse since the majority of their drivers are over 60 years old, putting them at a higher risk for serious illness.

Many didn't return to the job.

"That happened at the beginning of COVID, and it's just been ongoing. I'm sure that Omicron is not going to help the situation," she said. "We're only on day three of going back to in-classroom learning, so it's really hard to see if there's a trend if there are new cancellations or new delays."

Ryan Readings, chief administrative officer with Southwestern Ontario Student Transportation Services, confirmed that absenteeism of drivers has been a problem during the pandemic.

"It's becoming an issue as people are going into isolation and it's affecting both the regular drivers, the spare drivers or any bus company staff who otherwise could cover a route."

Readings said he couldn't speak to the recent school bus cancellations as he doesn't employ the drivers.

He recommended that parents subscribe to their cancellation and delay notifications on their website, My Big Yellow Bus, since disruptions to service will be "unavoidable" in the near future.

Bus driver shortages have been reported in other cities across Ontario like Ottawa and Kitchener-Waterloo.

"We're just asking people to be patient because this is a very difficult situation," said Daigneault. "There could be a great number of [drivers] getting ill in the next couple of weeks, and it just seems to be what's going on in all other sectors across Ontario. We're not alone."