How safe is air travel during COVID-19?

Authorities in Ireland may advise against air travel at Christmas, following a study suggesting 59 confirmed cases of COVID-19 could be traced back to a flight into the country during the summer months.

Ireland's Chief Medical Officer, Dr. Tony Holohan, has said "the risk of non-essential travel outside [the] country is simply too high at this moment."

In the study, published by Eurosurveillance, positive cases of SARS-CoV-2 were detected in passengers and contacts of passengers.

The flight into Ireland lasted seven-and-a-half hours. But it was only 17% occupied — 49 passengers on a 283-seat airplane. There were 12 crew members.

"Thirteen cases were passengers on the same flight to Ireland, each having transferred via a large international airport, flying into Europe from three different continents," write the study authors.

On the flight itself, passengers appear to have been relatively well distanced, apart from those people who may have been traveling as a group.

Some passengers reported spending up to 12 hours overnight in a transit lounge during a stopover, some shared a separate transit lounge, and others had separate short waits of under 2 hours in airport departure areas.

So, air travel isn't safe after all?

The Eurosurveillance findings appear to contradict previous advice that air travel on commercial flights is safe.

Airlines have been hit hard by the pandemic. Figures published by statista.com show the number of scheduled flights worldwide was down by 45.8 percent as of October 26, 2020, compared to the week of October 28, 2019.

As a result, there have been concerted efforts to boost public confidence in air travel.

There will have been an estimated 20 million flights by year end, which is still a significant number as it pertains to that single flight into Ireland and its 59 infections. We're only talking about one flight out of millions, and only 59 people out of about a billion potential annual air travelers. 

The report authors say themselves, that they "describe an outbreak that demonstrates in-flight transmission, providing further evidence to the small number of published studies in this area." Our italics.

It's also unclear whether the main point — or points — of viral transmission were the flight or busy airports, or both.

In a briefing, updated on October 21, the US Centers for Disease Control and Prevention (CDC) says "most viruses and other germs do not spread easily on flights because of how air circulates and is filtered on airplanes."

Read more: Germany mulls restrictions on traveling, partying

However, it goes onto say that "air travel requires spending time in security lines and airport terminals, which can bring you in close contact with other people and frequently touched surfaces. […] Social distancing is difficult on crowded flights and sitting within 6 feet [1.8 meters] of others, sometimes for hours, may increase your risk of getting COVID-19."

Meanwhile, on October 8, the International Air Transport Association (IATA), said "the risk of a passenger contracting COVID-19 while onboard [an airplane] appears very low." 

The IATA's Medical Advisor, Dr. David Powell, said that "with only 44 identified potential cases of flight-related transmission among 1.2 billion travelers, that's one case for every 27 million travelers. We recognize that this may be an underestimate but even if 90% of the cases were unreported, it would be one case for every 2.7 million travelers. We think these figures are extremely reassuring."

Further research on in-flight transmission

An article on MIT Medical, which is associated with the Massachusetts Institute of Technology, says air quality on commercial flights is "quite high" because it's refreshed regularly, within every five minutes.

Air circulation on airplanes moves from the top down and then out — it enters the cabin via overhead vents and exits via the floor. Some of that air is dumped outside and the rest is filtered using a hospital-grade system known as high-efficiency particulate air (HEPA) filters. That filtered air is then mixed with fresh air from outside the airplane before it's introduced into the cabin.

However, a 2018 study suggests that passengers and crew moving through the cabin during flight "may facilitate disease transmission," suggesting that the risks do not only lie in where you are seated — or socially distanced — from an infected person, but also whether you get up and go to the toilet, stretch your legs or talk to friends and family sitting elsewhere. 

The study authors write that "with over 3 billion airline passengers annually [as at 2018], the inflight transmission of infectious diseases is an important global health concern." But they go on to say that "the risks of transmission are unknown."

That was two years ago. Since then, knowledge about respiratory diseases, such as the novel coronavirus — the risks and their transmission routes — have grown.

But we are still dealing with a pandemic that seems to be changing before our eyes and as we experience it. So, it may be best to treat all new data as "to be confirmed."

Take, for instance, data released by the US Department of Defense earlier in October. It suggested the risk of exposure to the coronavirus in-flight was low.

Conducted on United Airlines Boeing 777 and Boeing 767 aircraft, the study found that while an average of 0.003% of air particles within the breathing zone around a person's head were infectious, even with a face mask, 99.99% of particles were filtered out of the air circulating in the cabin within six minutes. 

A United Airlines spokesperson described the chances of exposure to the coronavirus on one of their planes as "nearly non-existent, even if your flight is full."

So, how does that square with the flight into Ireland that was almost empty?

Boeing has also been keen to promote certain cleaning experiments it's done, for instance in collaboration with the University of Arizona. One includes the use of an electrostatic disinfectant spray and an "ultraviolet wand" to kill viruses on armrests, tray tables, overhead bins or lavatory handles.

They are, reportedly, showing that travel will be "safer tomorrow."

As for today, it may be best to err on the side of caution and limit your non-essential travel, as government health experts recommend, because the science is still very much out.