Read This Before You Fly Anywhere for the Holidays

Recent studies have deepened our understanding of in-flight Covid-19 risks

Photo: Darryl Brooks/EyeEm/Getty Images

After hitting a historic low in the first few months of the Covid-19 pandemic, the number of air travelers in the U.S has been slowly ratcheting up. On October 18, the Transportation Security Administration (TSA) screened over 1 million air travelers in a single day, an emblematic number that hadn’t been reached since March. With the holiday season approaching, even more people may be encouraged to hop on a plane to visit their families.

“I do have a general sense that people are getting a little tired of not traveling or being isolated from their family and friends. They are looking forward to the holidays to get back together,” says Henry Wu, MD, director of Emory TravelWell Center and associate professor of infectious diseases at Emory University School of Medicine. That, of course, is concerning given that Covid-19 numbers are hitting daily records in the U.S., having reached over 170,000 cases on November 13, and may continue to rise particularly with colder weather, according to Wu.

But here’s the good news: “We are learning a lot on how to prevent this infection on an aircraft […]. The precautions in place are certainly much better than they were early in this outbreak,” Wu says.

Over five months ago, when I first wrote about the risks of flying during the pandemic, there wasn’t strong evidence of SARS-CoV-2 transmission aboard an aircraft. But with more data available, this has changed. The International Air Transport Association (IATA) recently reported that, up until early October, there had been 44 reported cases of Covid-19 likely acquired during a flight.

One of the largest clusters connected with a flight was seen in passengers flying from London to Hanoi on March 2. A 27-year-old woman seated in business class experienced a sore throat and was coughing throughout the flight. When she was later diagnosed with Covid-19, a tracing effort revealed that 15 other passengers on that flight had been infected, 12 of whom were also in business class.

An important caveat: This happened back in March when masks were neither recommended nor widely used on airplanes. In fact, this was also the case in two other flights with Covid-19 mass transmission, according to a recent review. “The fact that these large clusters related to airplanes were early in the pandemic when not everyone was wearing a mask, and the fact that more recently there hasn’t been such large clusters, is another proof of the importance of wearing masks,” says Wu.

One notable example where masks probably prevented a superspreader event was a flight in February that repatriated 11 Israeli citizens who had been on the Diamond Princess cruise ship in Japan, where almost 20% of the ship’s population came down with Covid-19. All of the Israeli passengers who boarded the aircraft to go home tested negative in Japan before departure. “Still, we knew that they came from the Diamond Princess and we were reluctant with the fact that they were flying and anticipated that one or two could be positive,” says Ran Nir-Paz, MD, associate professor at the department of clinical microbiology and infectious diseases at the Hadassah-Hebrew University Medical Centre.

“Overall the risk is very low, as most of the aerosol is removed, even nearby an infected person, before it can settle out on a surface.”

They were instructed to wear masks at all times, even when sleeping, only removing it for a brief period to eat and drink. Upon arrival, they were retested and two of them were found to be positive. The investigation later showed that they were probably infected before boarding and were infectious during the flight (in the first few days of infection, before the virus builds up to detectable levels, there is a high probability of a false negative result, which could explain why their predeparture tests came back negative). Still, no other passenger got sick.

“We assumed that the major intervention was the fact that they were wearing masks most of the time,” says Nir-Paz. Given that this was a 14-hour long flight, the fact that nobody else got infected despite so much time in close proximity to the two passengers with Covid-19 is reassuring.

An airplane’s ventilation system is also quite effective in eliminating viruses and other germs. The filters used on planes, called high-efficiency particulate air (HEPA) filters, are able to remove beyond 99% of infectious pathogens.

A more recent study conducted for the Department of Defense by researchers from several institutions and organizations, including United Airlines and Boeing (which may raise awareness for potential bias), simulated how the virus would likely spread through the plane’s cabin. The tests involved placing an “infected passenger” (a masked mannequin expelling fluorescent microspheres made of a synthetic material roughly the same size as the novel coronavirus) in different rows and seats to determine how far those particles would be able to reach and how long would it take for them to be filtered out.

Image provided by the U.S. Transportation Command by permission

The tests showed that, on an airplane, microparticles are removed from the air 15 times faster than in a typical house: six minutes on the airplane versus 1.5 hours in the house. Does that mean that the risk of transmission is lower on an airplane compared with other enclosed spaces?

“Yes, for a similar number of sick people located at a similar distance, the risk is definitely lower because of the very high air exchange rate, downward ventilation design, and HEPA filtered recirculation,” says Sean Kinahan, senior threat scientist at the National Strategic Research Institute at the University of Nebraska and one of the authors of the study.

They also measured the number of particles on contaminated surfaces. “Overall the risk is very low, as most of the aerosol is removed, even nearby an infected person, before it can settle out on a surface,” Kinahan says. The study concluded that, in a situation where all flyers are wearing masks, the risk of virus transmission is minimal, even if the airplane is at full seating capacity.

Try to reduce the time of your meal to 15 minutes or less and, if there are other passengers eating around you, wait for them to be finished and put their masks back on before you remove your own mask to eat.

All of this recent knowledge about the risk of SARS-CoV-2 transmission aboard aircrafts might help you decide whether you want to fly during the pandemic. In general, experts encourage people to have a higher threshold for evaluating their need to travel this year. “Don’t rush to book a trip just because you feel like you need a vacation,” says Claire Westmacott, MPH, a public health specialist at the International Association for Medical Assistance to Travellers (IAMAT). “Travelers have to be aware of their responsibility and their privilege, and travel very carefully.”

Here is some more advice to help you stay safe if you do choose to travel.

Planning your trip

  • Several destinations have restrictions or requirements in place for incoming travelers, such as providing proof of a recent negative PCR test or proof of travel health insurance. Some even specifically require proof of Covid-19 related coverage, according to Westmacott. If you are traveling internationally, your best resource is IATA’s interactive map, where you can click on any country to find out about possible restrictions. Domestic travelers can check their destination’s state health department for up-to-date guidance.
  • Remember that you have a social responsibility to quarantine upon arrival at your destination and when returning home, and many locations explicitly require it, so prepare accordingly. In some locations like the state of New York, out-of-state travelers may exit quarantine sooner if they follow certain testing guidelines.
  • Keep in mind there may be abrupt changes to your travel plans. “Particularly the possibility that travelers may have to stay at their destination for a much longer period of time than they anticipated, for example, if they’re exposed to the virus, or they become sick themselves and have to quarantine before returning,” says Westmacott.
  • On that note, Westmacott advises considering your own personal ability to handle uncertainty and stress and how much financial risk you are willing to take.
  • Be aware of increased negative attitudes toward visitors. “At this time, travelers really need to ensure that they’re making responsible choices and being conscious of their impact on the communities that they visit,” Westmacott says.
  • Get the influenza shot, if you haven’t already. Although it doesn’t protect against Covid-19, influenza can be quite common during travel, notes Wu. “Influenza and Covid-19 can look very similar. So, it can cause a lot of problems if you were to develop influenza during your trip,” he says.
  • Don’t travel if you are feeling sick or have been in contact with a Covid-19 patient 14 days prior to the trip.

Keeping safe inside the airplane

  • Wear a face mask, even when sleeping, and only remove it when you need to eat or drink.
  • Keep sanitizer handy and use it often, including before and after eating or adjusting your mask.
  • Try to reduce the time of your meal to 15 minutes or less and, if there are other passengers eating around you, wait for them to be finished and put their masks back on before you remove your own mask to eat.
  • Wipe down your seat, tray table, and armrest with a disinfectant wipe. “You can be pretty sure that they’ve been cleaned before you boarded but, just in case, it’s a good thing to do,” says Westmacott.
  • If you need to go to the lavatory, try to wait for a moment when there is no line. You may also wipe surfaces with a disinfectant wipe before touching them. Needless to say, wash your hands thoroughly before returning to your seat.

Science and health journalist with a special interest in evidence-based medicine and epidemics. Columbia Journalism School alumna. mari.lenharo@gmail.com.

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