Coronavirus: what are the odds of catching Covid-19 on a plane?

Air travel while wearing a face mask is safer than previously believed, a US government study has found.

Researchers at the US Transportation Command and Air Mobility Command put two United aircraft, a Boeing 777 and a Boeing 767, through 38 hours of flight time and 45 hours of testing on the ground.

Over 180 million fluorescent aerosol tracers were “exhaled” by a mannequin called Ruth during 300 aerosol tests, both with and without a mask. The seats surrounding Ruth contained sensors representing other passengers.

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Only 0.003% of particles - or one in every 33,000 particles - made their way into another passenger’s breathing zone when the source of the infection is seated and wearing a mask. Around 99.99% of all particles were filtered out of the cabin air within six minutes due to air circulation, ventilation and filtration.

The travel news website Head For Points says evidence is “mounting” that aircraft themselves are very safe provided masks are worn, though the airport itself or any public transport taken to get to the airport may be riskier.

What about the other evidence?

“The Covid-19 coronavirus is still relatively new, so accurate data on how it can spread between aircraft passengers is in short supply,” the BBC said back in June.

Yet while scientists are still cautious, the data collected so far is reassuring.

“In one case, about 328 passengers and crew members were tested for coronavirus after it was learned that a 31 March flight from the US to Taiwan had been carrying 12 passengers who were symptomatic at the time,” CNN reports. “However, all the other passengers tested negative, as did the crew members.”

Other research has found that even if a flight is carrying a “patient zero”, cabin filtration and ventilation systems mean the chances of picking up an infection are between 0% and 1% “for the vast majority of all passengers, apart from those sitting on the same row or across the aisle”, says The Independent.

If everyone is wearing a mask, as most airlines now require, the risk is reduced still further. Other PPE, including plastic visors or face shields, may be even more effective.

“The science is changing every day,” Massachusetts Institute of Technology (MIT) statistician Arnold Barnett told CNN, “but my understanding is, if you wear a mask, it greatly reduces the chance of you infecting others, but it doesn't protect you all that much. Whereas a shield will protect you.”

Barnett put the chance of catching Covid-19 on a full short-haul flight at one in 4,300.

So is it safe to fly?

Not completely, but more so than you might think. Mixing with a large number of people is certain to increase the risk of infection - and there are confirmed cases of people contracting Covid-19 on aircraft.

A US Centers for Disease Control study looked at data on 310 passengers and crew who were on an evacuation flight from Italy to Korea in late March.

Social distancing was maintained before boarding, and “11 symptomatic passengers were removed from the flight”. Yet despite these measures, and the use of protective equipment, one women contracted the disease while aboard.

Although this woman “wore an N95 mask” for most of the flight, the study says, she removed it while using a “toilet [that] was shared by passengers sitting nearby, including an asymptomatic patient”.

The “most plausible explanation” for her contracting Covid is that she inhaled droplets containing the virus while in the confined space of the aircraft toilet, the researchers conclude.