Hundreds of flights in the United States, and dozens at Boston’s Logan International Airport, have been canceled on Christmas Eve amid airline staffing shortages caused by COVID-19 outbreaks.

U.S.-based Delta Air Lines and United Airlines said they had to cancel dozens of Christmas Eve flights because of staff shortages tied to the omicron variant. United canceled 176 flights, Delta canceled 145 and JetBlue called off 71, as of Friday morning, according to flight tracker FlightAware. More than 3,400 flights have been canceled globally for Friday and Saturday.

As of 11 a.m. Friday — Christmas Eve — a total of 33 flights were canceled at Boston’s Logan International Airport, 16 departing and 17 arriving, according to FlightAware. Twenty-three of those flights were JetBlue.

Jennifer Mehigan, media relations director for MassPort, which operates Logan Airport, encouraged passengers to check with their airlines about their flight status before heading to the airport.

“The nationwide spike in omicron cases this week has had a direct impact on our flight crews and the people who run our operation,” United said in a statement. “As a result, we’ve unfortunately had to cancel some flights and are notifying impacted customers in advance of them coming to the airport.”

The airline said it was working to rebook as many people as possible.

Delta said it canceled flights Friday because of the impact of omicron and possibility of bad weather after it had “exhausted all options and resources — including rerouting and substitutions of aircraft and crews to cover scheduled flying.”

It said in a statement that it was trying to get passengers to their destinations quickly.

The cancellations come as coronavirus infections fueled by the new variant further squeeze staffing at hospitals, police departments, supermarkets and other critical operations struggling to maintain a full contingent of front-line workers.

Germany-based Lufthansa said Friday that it was canceling a dozen long-haul transatlantic flights over the Christmas holiday period because of a “massive rise” in sick leave among pilots. The cancellations on flights to Houston, Boston and Washington come despite a “large buffer” of additional staff for the period.

The airline says it couldn't speculate on whether COVID-19 infections or quarantines were responsible because it was not informed about the sort of illness. Passengers were booked on other flights.

Lufthansa said in a statement that “we planned a very large buffer for the vacation period. But this was not sufficient due to the high rate of people calling in sick.”

Reporting from the Associated Press was used in this article.