Coronavirus spread on planes

Recently, all 193 travellers returning on a flight back to the UK from Zante were told to quarantine themselves for a fortnight after 16 people tested positive for coronavirus. TUI, the operator, are urgently investigating practices on the flight that might have contributed to the outbreak. So how safe are aeroplanes? The World Health Organisation suggests that transmission is limited to a couple of rows either side of an infected case. The University of Leicester’s Julian Tang specialises in the airborne spread of viral infections...

Julian - The highest risk, looking at the airflow dynamics of exhaled breath, is when they're directly beside you. If they're in front of you and behind you, the deflection effect of the seats will actually, probably, deflect a lot of the aerosol upwards, where the aeroplane ventilation - which is very efficient - can actually remove that exhaled aerosol. And the ventilation in planes is typically 20 to 30 air changes per hour, which means they can remove and replace the whole of the cabin air volume within two to three minutes, and remove that airborne virus away very quickly. But if you can smell your neighbour's garlic breath or alcohol after their meal, you then have enough air to transport airborne virus within that short distance between you before the ventilation can actually whisk it away.

Chris - Where does the air actually flow in an aircraft? Does it come from above and disappear through the floor, or does it sort of mix up like a giant washing machine?

Julian - Essentially this is a very strong airflow, they're counter rotating currents coming from above your head and drawn down underneath your feet. Different planes have slightly different flow patterns, but generally they are designed to prevent longitudinal flow of any airborne contaminant down the length of the plane. So they're like a series of counter rotating flows all the way down the plane to limit that forward-backward transmission. Unfortunately they're probably not efficient at the close range conversational contact distance that you have talking to your neighbour to whisk that air away sufficiently quickly.

Chris - And of course there's the whole issue of the airport itself, isn't there? Because while the aeroplane may well have these measures in place, there isn't a similar sort of thing in the airport building, where you might have people lingering together for prolonged periods of time sharing air.

Julian - Exactly. So it's very hard to actually decide where a person who's infected acquired the infection from, particularly if you're two hours pre-boarding and one to two hours de-planing to pick up your luggage, you're standing beside somebody at the Customs security gates, or picking up your luggage that may actually transmit the infection to you. And when they test you three to five days later, it's very hard to tell where you actually got that infection from because of that close temporal proximity of those potential contacts.

Chris - So in your view then - given that planes have all these measures in place but, say, trains and buses don't - do you think you're safer on a plane than you are on the train to London?

Julian - I think if everybody is masking, given a similar baseline, I think the plane would be a safer place. The only disadvantage with a plane is that you have 200 to 300 passengers in a very, very tight space, whereas on a train or a bus you might be able to spread yourselves out a bit more, plus you can open windows for example. So the plane is really a captive audience of high density; you rely a lot on the mechanical ventilation, which has been filtered, which is not on trains or buses typically; and you rely on your fellow passengers to keep their masks on to reduce transmission in that very tight, confined area.

Chris - Of course it's easy to say but hard to do, isn't it? If you need to eat, you need to drink, you need to do various things, you might not be able to maintain a hundred percent masking. Especially if you're in a long flight.

Julian - Exactly. And that's why, unfortunately, outbreaks like this are probably inevitable. When you've got 100 million to a billion passengers travelling by air over a course of a year, you may unfortunately see a few of these clusters, especially with this virus which seems to be much more transmissible; and mutations in the virus spike protein suggest it’s becoming more transmissible, adapting to the human population, going forward. But hopefully if you can maybe stagger the eating times amongst the passengers so some of them can keep their masks on while others are eating, you can reduce this transmission rate further.

Chris - Are there any tips that you could offer to our listeners so that if they are destined to take a flight in the near future, they can minimise any risks that might come from their trip abroad?

Julian - One thing I've been thinking about doing is that, if the main risk has been taking the mask off to eat or to have refreshment, if you can try and time that when your neighbours - your immediate neighbours left and right of you - are not doing the same, that's probably the thing I would consider doing, because they're the most risk in terms of being a source of the virus. The air hostesses do collect the trays on a regular basis, so they may have to stagger the distribution of the food trays, refreshment trays, at different times so passengers can actually stagger their eating; but I don't know how easy that is to do, particularly if their flight is not that long and they have to dish out the refreshment in a timely manner. Also if you can not talk to your neighbour, not talk when you're waiting at the toilet - be antisocial, because talking is actually a risk - that would minimise your exposure and the exposure to other passengers from your breath.