For the fourth day in a row, hundreds of flights are canceled across the US

There were more than 1,000 flights canceled Monday within, into or out of the US. The country has seen well over 3,000 flights canceled over the Christmas holiday the past four days. 

Weather is playing a part in some areas such as the Pacific Northwest, but major airlines are also blaming the spread of the omicron variant. Airline employees are getting sick, creating a staffing shortage. 

At San Francisco International Airport, at least 70 flights we canceled Monday, following 69 cancellations on Sunday. 

"I had originally a five-hour layover, which turned into like an 11-hour layover, and then the flight got canceled. So back today to try to get on another one out today," said David Doran. 

Doran has been at SFO for almost two days. He's hoping his trip from Ireland to San Diego will end with him actually seeing the family members he's trying to visit. 

"What can you do? You just have to roll with the punches I guess, and I feel sorry for some of the air staff people as well because they’re getting so much grief. Obviously so many people are disappointed they’re not able to get to where they need to go, but all you can do is wait and hope that it works out," said Doran. 

At SFO, lines are full of passengers trying to get rebooked after being notified their flight is one of the thousands canceled this holiday weekend. 

"They said for me to watch my email, and that’s why we’re here. I have called Alaska (Airlines) and I’m waiting for a call back from them, I’m in line here and I’ve already rebooked on another airline," said Marjorie Winter.

A shortage of airline staff, likely a direct impact of COVID, has the Winter family's trip to Mexico for their son's birthday postponed. 

"Whenever you fly during the holidays you always have to prepare for delays, cancellations, trip interruptions," said Winter. 

A group of leaders at major airlines has been asking the CDC to change its guidance on quarantining from 10 days to five days, in hopes that would help prevent some of the staffing issues we are seeing now. 

On Monday, the CDC updated its guidance to reflect that change, not only airline workers, but for everyone. 

Dr. Peter Chin-Hong, an infectious disease specialist at UCSF, said the update in guidance could help with the crisis we are in. 

"It’s not a crisis so much as people dying, which is very different from a year ago. But it’s a crisis in terms of not having a work force," said Chin-Hong. 

But he said five days of quarantine won't work for everyone.

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"When you talk about 10 days, pretty much more than 90% of people will be fine. You don’t really need to do a test for the guidance. But when you talk about five days, some people are fine, some people are not fine. You really need to take people’s symptoms into consideration and use a test to help guide you," said Chin-Hong.

While the new recommendation means pilots and flight attendants can get back to work quicker, Dr. Chin-Hong hopes employees won't be forced to return to work if they still don't feel good. 

And Dr. Anthony Fauci said Monday the US might want to think about mandating vaccination for domestic flights – not just international ones. 

"That is just another one of the requirements that I think is reasonable to consider," said Fauci.