How Safe Is Flying in the Age of Coronavirus?: QuickTake

(Bloomberg) -- How safe is it to fly? This remains a troubling question. The hopes of airlines for a rebound in travel after an initial collapse ran up against a resurgence of SARS-CoV-2 around the world starting in late 2020. Overall, the demand for flights fell in 2020 by a record 66%, as measured by the number of kilometers traveled by paying passengers, according to the International Air Transport Association. Quarantines and travel restrictions account for much of the slide, but in addition, would-be passengers continue to worry about being stuck in a cabin for an extended time with possibly infectious strangers. The evidence shows the risks aren’t negligible.

1. How many fliers have caught the virus?

It’s impossible to know. IATA, the trade group for the world’s airlines, counted 44 confirmed or suspected instances of in-flight transmission in the first nine months of 2020. With 1.2 billion passengers traveling in that period, the group said the risk appeared to be “very low.” However, its count was not comprehensive, and independent researchers caution that any tally of known cases is likely to reflect the difficulty establishing the spread of a virus on a plane.

2. Why is it hard to establish?

It involves knowing a passenger was infected, interviewing and testing as many as hundreds of fellow fliers, then, ideally, analyzing the genomes of any additional viruses that turn up to check for connections to the first passenger’s infection. That’s a huge research project, impossible to undertake with every known case of someone flying while capable of infecting others with SARS-CoV-2. In early 2021, on average there were three flights a day in or out of Canada alone that contained someone confirmed to have Covid during a period when they may have been infectious, according to a website maintained by the country’s health authorities.

3. What can make flying risky?

As with other forms of public transport, the risk comes from close proximity to others and surfaces touched by many people. Those infected with the novel coronavirus emit virus-containing droplets from their noses and mouths that can be transferred directly to someone nearby or picked up from a contaminated surface and conveyed to the mouth, nose or eyes. Studies of other viruses that spread the same way have found that the greatest risk on a flight comes from sitting within two rows of a contagious person for longer than eight hours. The authors of a study on the risks published in the Journal of Travel Medicine in November recommended that passengers wear a face mask; use disinfectant to wipe down headrests, tray tables and arm rests; make frequent use of hand sanitizer; and take special care while entering and exiting the plane to avoid touching seat backs and maintain a distance from other people. Navigating the airport also requires vigilance as travelers wait in queues, check in for flights, visit food vendors and use bathrooms.

4. What about airborne transmission?

The coronavirus also can be transmitted via smaller particles that people emit from their noses and mouths. Known as aerosols, they can float through the air and be inhaled. The airline industry says modern aircraft ventilation should mitigate the risk of this sort of spread. The air on a plane is generally a 50-50 mix of sterile outside air and recirculated cabin air that’s been filtered. Airbus SE and Boeing Co., the world’s two biggest planemakers, say that since the 1980s they have been fitting their aircraft with HEPA filters, which capture particles as small as the virus. Some older aircraft, however, use less efficient filters. Cabin airflow goes from ceiling to floor rather than front to back and is split into sections, which should limit the movement of particles along the length of the plane. Even so, modeling suggests this airflow can be influenced by factors such as seat and cabin layout and how full the aircraft is. Also, these ventilation systems may not be fully operational when planes are parked at the gate; an influenza outbreak in 1979 resulted from passengers being kept on board a grounded aircraft with the ventilation turned off. Some airlines say they are now keeping the systems turned on until everyone exits the aircraft.

5. Does it help to turn on the personal air vent?

It’s not clear. The planemaker Embraer recommends that fliers use the vent, also known as a gasper, to blow air directly toward their seats. The company said its tests show this creates an airflow routing particles to the air-return grills on the cabin floor and minimizing contamination between rows. But a 2020 study led by the U.S. Defense Department’s Transportation Command concluded that whether the gasper is off or on has no significant impact on the risk of aerosol transmission on planes.

6. Are airplane lavatories especially dangerous?

In August 2020, U.S. health authorities confirmed a report of a woman who contracted SARS-CoV-2 from a fellow passenger during a flight from Italy to South Korea, most likely while using the onboard toilet with her mask off. This provoked speculation that the toilet’s flush had spread SARS-CoV-2, which has been found in feces. A study of the fluid dynamics of regular toilets, which use a siphoning effect to suck the contents of the bowl down a sewer pipe, concluded that flushing does propel virus particles above the toilet seat. Airplanes, however, use vacuum toilets, which use suction to pull waste out of the bowl using a fraction of the water required in conventional models. In any case, the authors of the article in the Journal of Travel Medicine recommended that fliers keep their masks on in the lavatory, clean the toilet seat before using it, close the lid before flushing, wash their hands carefully after flushing and sanitize their hands after touching the door handle.

7. What are airlines doing to mitigate risks?

They are now telling customers to wear face masks throughout their journeys, which can reduce risks. The airline trade group notes that most published cases of inflight transmission occurred before this happened. Still, in many instances the rule is not strictly enforced, and mask-wearers have become infected. For example, researchers concluded that a man on a flight from Singapore to China on Jan. 21, 2020, who let his mask slip while chatting to his wife and son, was probably infected by fellow fliers. Airlines are also cleaning aircraft more frequently and thoroughly, going cashless, and using online check-in and automated bag drops. Some are no longer serving food and beverages, and passengers are being asked not to queue for the toilet. In the U.S., only Delta Air Lines Inc. promises to always leave space between passengers, though other carriers are limiting the numbers on each flight, when possible. European airlines have largely been reluctant to commit to leaving middle seats empty, saying that the science is limited on the effectiveness of the practice and that it would make flights too costly to run.

8. How does the availability of Covid-19 vaccines affect things?

Eventually, the widespread distribution of vaccines should help significantly reduce infection rates, which will make any encounter with other people -- including on airplanes -- safer. The chief executive officer of Australian airline Qantas Airways Ltd., Alan Joyce, has said his company plans to require international travelers entering or leaving Australia to present proof of vaccination before boarding. Joyce said he expects other carriers to do the same. Although the vaccines that have been authorized for use have been shown to provide significant protection against becoming sick from a SARS-CoV-2 infection, for most of them, it’s not yet known whether they will prevent someone from getting an asymptomatic infection and spreading the virus. There are also questions about how well they work against newly emerged strains of SARS-CoV-2 that studies suggest are more contagious.

The Reference Shelf

• Related QuickTakes on how the virus spreads, what vaccines can and can’t do, coronavirus mutations and masking up.
• An article in Journal of Travel Medicine on navigating the risks of flying during the pandemic.
• The Canadian government’s website listing flights that contained someone capable of spreading SARS-CoV-2.

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