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How safe is air travel?

MIT Medical answers your COVID-19 questions. Got a question about COVID-19? Send it to us at CovidQ@mit.edu, and we’ll do our best to provide an answer.

I’m anxious to visit my parents, but I’m wondering how safe it is to fly right now. With all the talk about the virus being airborne, how dangerous is the re-circulated air in the cabin? Is it worth booking with an airline that blocks middle seats? And are there other risks I’m not even considering?

Illustration of a cross-section of an airplane showing a row of seats with every other seat occupied by passengers wearing PPE masks and arrows indicating the direction of airflow in the cabin

At first thought, a narrow metal tube in which strangers are crammed together for hours might seem like a flying petri dish, especially during a pandemic. The reality is a bit more nuanced. While there are risks associated with flying, it may be safer than you think.

For starters, the air quality on a commercial airliner is actually quite high, with the air volume in the cabin being completely refreshed every two to four minutes. Air flows into the cabin vertically — it enters from overhead vents and is sent downward in a circular motion, exiting at floor level. Once air leaves the cabin, about half is dumped outside, and the rest is sent through HEPA (high-efficiency particulate air) filters, similar to those used in hospitals, before being mixed with fresh outside air and entering the cabin again.

Of course, passengers and crewmembers moving up and down the aisles can disrupt this airflow, altering the path of any airborne particles. And while the HEPA filters used in commercial aviation can filter out 99.97% of virus-sized particles, they can’t capture every respiratory droplet or viral aerosol before someone else inhales it.

Still, the design of air-handling systems on commercial aircraft makes it unlikely that you’ll be breathing in air from anyone more than a few rows away. In fact, a 2018 study that examined the transmission of droplet-mediated respiratory illnesses during transcontinental flights found that an infectious passenger with influenza or another droplet-transmitted respiratory infection was highly unlikely to infect passengers seated farther away than two seats on either side or one row in front or in back.

And that was without masks.

Your flight will be even safer if your airline requires all passengers and crewmembers to wear face coverings, which are designed to contain respiratory droplets before they can be expelled into the air. There’s real-world evidence that masks on planes can make a difference. Early in the coronavirus pandemic, a man flew from Wuhan to Toronto with a dry cough and subsequently tested positive for COVID-19. He wore a mask during the flight, and no other passengers were infected. 

True social distancing on a plane is impossible, but, as you note, some airlines are currently leaving middle seats unsold, creating a bit more space between passengers. So is it worth trying to book your flight with one of those carriers? Arnold Barnett, the George Eastman Professor of Management Science and a statistics professor at MIT’s Sloan School of Management might answer “yes.” In an as-yet unpublished analysis, Barnett, an expert in mathematical modeling who focuses on issues of health and safety, concludes that there is “a measurable reduction in COVID-19 risk when middle seats on aircraft are deliberately kept open.”

Barnett used an average of the infection rates in New York and Texas in early July to estimate the probability that any given passenger on board would be infectious and assumed universal masking. However, he did not consider the odds of passengers becoming infected during boarding, deplaning, or moving about the cabin during flight; the possibility of transmission between rows; or how the odds might change with longer or shorter flights. While Barnett acknowledges these potential shortcomings and the “rudimentary” nature of his calculations, he estimates that blocking out the middle seat on airplanes would reduce the likelihood of COVID-19 infection by nearly half.

However, as many have pointed out, leaving middle seats empty is not a viable, long-term business model for an industry with razor-thin profit margins. But some airlines that have resumed selling middle seats have also committed to informing travelers when their flights are reaching capacity, allowing them to rebook on less crowded flights without penalty. Airline policies are constantly changing, so be sure to double-check your airline’s current stance before buying a ticket.

And whatever your airline’s middle-seat policy may be, when it comes to the risk of contracting an illness in flight, a window seat may be your safest bet. Having a wall on one side automatically reduces your number of close-proximity contacts. A window seat also protects you from the inadvertent close contacts that can occur when other passengers are hoisting bags into overhead bins at the start of a flight or crowding aisles to deplane after landing.

Even with appropriate precautions, a relatively short domestic flight still carries moderate risks and should not be undertaken lightly. And, as the CDC notes, the risks don’t begin and end with the flight itself. You should also consider the prevalence of the virus in your community and the community to which you’re traveling, your own risk of severe illness from COVID-19 or the risks to vulnerable members of your household, and quarantine requirements at your destination or when you return home. MIT Medical continues to recommend that you postpone nonessential travel at this time, but if you must travel, do your best to travel thoughtfully, safely, and with deliberate attention to your own safety and the safety of others.

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