Airports are preparing for a crush of passengers as holiday air travel in 2021 is expected to approach pre-pandemic levels.
More than 6 million people are expected to fly between Dec. 23 and Jan. 2., with airlines projected to see a 184% increase in passengers from 2020, according to AAA, which called it a "dramatic bounce-back."
"With vaccines widely available, conditions are much different and many people feel a greater level of comfort with travel," said Paula Twidale, senior vice president of AAA Travel, in a statement.
Holiday bookings for Christmas and the New Year's holiday have been coming in "very, very strong," Ed Bastian, the CEO of Delta Air Lines, told CNBC. United has been flying its largest schedule since the start of the pandemic, adding more than 200 daily domestic flights to meet the increased demand.
More than 2 million people passed through Transportation Security Administration checkpoints on Dec. 16, 2021 — more than double the passenger volume on the same day in 2020.
But the rapid spread of the omicron variant may have many people wondering: Is it safe to fly right now?
'Very low' risk
There's not a one-size-fits-all answer to that question — it all depends on a person's risk tolerance and their own risk factors for severe disease, said Dr. Amesh Adalja, a senior scholar at the Johns Hopkins University Center for Health Security in Baltimore and a spokesman for the Infectious Diseases Society of America.
Masks are required on planes and at airports, and as long as people are complying, there's not a major risk from flying, he noted.
"Transmission on a plane of COVID-19 is not very common because of the (air) circulation and because of the mask wearing," Adalja told TODAY.
"(But) there's always going to be some level of COVID risk with any activity you do, whether it's flying, riding the bus or going to the post office... for most people, I think it's an acceptable risk."
The more vaccinated passengers and crew are on a plane, the safer air travel is, Adalja added, so he was a fan of airlines mandating vaccinations as a condition of employment, the way United Airlines has.
Masking and vaccines are the best tools we have against both the omicron and delta variants, he said.
The Centers for Disease Control and Prevention urged people to delay travel until they were fully vaccinated. If that's not possible, they should get tested one to three days before their trip.
Given the high quality of cabin air and the various safety measures in place, there is "very low" risk of contracting COVID-19 on board a plane, according to the International Air Transport Association, which represents airlines around the world.
What studies have found:
United Airlines and the Department of Defense teamed up on a six-month study that found the risk of contracting COVID-19 on commercial flights was low when passengers wore masks for the entirety of the flight. The highest risk was associated with sitting in the same row, or a row in front of or behind, an infected person. This study didn't take into account the risk associated with being in a crowded airport or boarding a flight.
Researchers have said factors that may prevent transmission on planes include the airflow in the cabin from the ceiling to the floor and all passengers wearing face coverings.
But if everyone took off their masks at the same time for a one-hour in-flight meal service, the average infection probability increased by 59%, a study published in the Journal of Travel Medicine in May 2021 found.
Still, most viruses don’t spread easily on flights because of how air circulates and is filtered on planes, the CDC noted.
Carriers like American Airlines have been touting the use of high-efficiency particulate air (HEPA) filters on board that capture “at least 99.97% of airborne microbes by circulating the cabin air once every 2 to 4 minutes.”
Airlines have also implemented enhanced cleanings and traveler health acknowledgments during check-in.
A paper by Arnold Barnett, a statistics professor at the MIT Sloan School of Management in Cambridge, Massachusetts, looked at the probability of an air traveler contracting COVID-19 from a nearby passenger while sitting in economy class on a two-hour domestic U.S. flight. He assumed everyone was wearing masks.
Barnett calculated the risk at 1 in 4,300 for full flights, which went down to 1 in 7,700 when middle seats were kept empty.
It's not clear that two hours spent on a plane involved a higher COVID-19 infection risk than two hours doing any other everyday activities during the pandemic, Barnett concluded in the study.
"You don't get sick on airplanes any more than anywhere else," wrote Joseph Allen, an assistant professor of exposure assessment science at Harvard T.H. Chan School of Public Health in Boston, in The Washington Post. "The required aircraft systems do a really good job of controlling airborne bacteria and viruses."
Danger on the ground
Experts have been more worried about coronavirus spread before flights.
“My concern has really been in the airports funneling people through hallways and jet ways and metal detectors,” said Dr. Michael Mina, an epidemiologist at Harvard T. H. Chan School of Public Health, during a briefing in 2020. “The whole process of airports… and squishing people together. We know that this virus can be airborne and it can linger for a little bit.”
Any part of the trip where you can’t social distance is more risky since the virus transmits most efficiently when people are in close contact together, including at the airport food court and standing at the gate before boarding, Adalja added. He also believed people’s behavior at the destination was usually riskier than the journey itself.
If you plan to fly soon, Adalja recommended taking all the usual precautions during the trip: Wash your hands frequently, wear a face covering as required, avoid the crowded parts of the airport and try to stay 6 feet apart from everybody. Always have hand sanitizer with you.
Some studies have found the window seat may be best to avoid getting sick because it offers the least contact with other passengers, but Adalja was skeptical. It all depends on who's sitting beside you since it’s usually 10-15 minutes of close proximity — not fleeting contact — that transmits the new coronavirus virus, he said.
If you’re more likely to get the severe form of COVID-19, consider if it's worth the risk to fly. Don't fly if you're sick or have been in contact with someone who is sick. These are all important things to keep in mind during the holiday travel season.
This article was updated in December 2021 to include the most recent research and statistics.