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What SARS and 5 deaths on Air China Flight 112 showed about disease transmission whilst flying

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Whilst we haven’t covered it, there has been quite a bit of discussion in recent days over easyJet’s plan to leave all middle seats empty when it resumes flying.

The airline believes that its plan will reduce the risk of coronavirus transmission on board.  In reality, I think that easyJet knows that it won’t be selling more than 2/3rd of its seats for quite a while and that this is simply easy publicity to reassure people.

If it does reassure you, it possibly shouldn’t.

We have been here before, with SARS.  In particular, the infamous (if you’re a clinician) case of Air China flight 112 from Hong Kong to Beijing in March 2003.

The flight length was three hours, which is worth bearing in mind as you read on.  Until this flight, it was assumed that mass infection would require a minimum flight time of eight hours and that only passengers within two rows of the source were at risk.

Take a look at this image.  This is taken from Flyertalk.  I can’t find the original source but there is an identical seatmap – just not as easy to follow – in The New England Journal of Medicine here.

Air China flight 112

What you can see from this seatmap is that, in Row 14, was a 72 year old man with an active case of SARS.  He later died.

The general view at the time, as shown in the pink area, is that anyone who was sitting within two rows of an infected person – in front or behind – was at risk.

However, as you can see from the dots, passengers were infected up to seven rows from the infected passenger.  In total, 22 people were infected with SARS during the flight and five died.

(There are not 22 dots on the image above because it was not possible to confirm where two passengers had been sitting.  The total of 22 also includes two members of cabin crew.  These two members of cabin crew were both from Mongolia and were belived to be directly responsible for a further 300 infections in Mongolia.)

To put this in context, total global deaths from the 2003 SARS outbreak totalled 774.  This single flight accounted for 0.65% of global deaths, excluding the original infected passenger.

All 22 infected people developed symptoms within two to eight days of the flight.  None had any known additional exposure to anyone with SARS.  Whilst some of the infected passengers were travelling together, only one of the 22 cases developed so late (eight days post flight) that it could potentially have been due to secondary infection.

Air China flight 112

It isn’t that simple of course …..

The New England Journal of Medicine report is worth reading, because it also looks at two other flights taken by known SARS carriers.

One flight, which had four known carriers on it, only led to one additional infection.

A second flight, with a passenger who was not showing symptoms at the time of travel, led to no additional infections.  This flight was carrying 315 passengers on a Boeing 777.  74 passengers were interviewed directly to confirm they had no symptons and enquiries were made into the health of the others.

You should not assume that it is unavoidable that an infected person will infect others whilst travelling.

Here is a relevant paragraph from the report above about Flight 112:

The risk of illness was related to the proximity to the index patient, with illness reported in 8 of the 23 passengers who were seated in the same row as the patient or in the three rows in front of him, as compared with 10 of the 88 passengers who were seated elsewhere (relative risk, 3.1; 95 percent confidence interval, 1.4 to 6.9). It is notable that 56 percent of the passengers who became infected were not seated in the same row as the index patient or in the three rows in front of him.

In terms of actual seating:

There was no significant difference in risk between persons seated in an aisle seat and those seated in a middle or window seat (6 of 39 [15 percent] vs. 12 of 72 [17 percent]; relative risk, 0.9; 95 percent confidence interval, 0.4 to 2.3). Two of the 20 passengers who became infected (and whose seating assignments are known) were seated within 0.9 m (36 in.) of the index patient.

The fact that most of the infected passengers were sat in front of the index passenger is what would have been expected for a disease spread by droplets released during breathing.  This should not have impacted passengers more than three feet from the infected passenger, based on assumed guidelines, but more than 90% of infected passengers were sat further away than this.

There are, of course, other potential ways in which passengers could have been infected – during or immediately after boarding, after disembarking at immigration or baggage reclaim, or moving around the aircraft during the flight.

Air China Flight 112

It’s not all bad news ….

The good news, to some extent, is that Flight 112 has become infamous simply because it is so rare.  The passenger involved is believed to have been a ‘super spreader’ who was substantially more likely than average to infect others.

The New England Journal of Medicine report concludes that:

It seems likely that the overall risk to airline passengers is quite low. As of May 12, 2003, the WHO reported that 35 flights were under investigation because a patient with symptomatic SARS had been on board, but only 4 of these flights were deemed to be associated with possible transmission.  Aircraft ventilation systems are believed to be highly efficient at keeping the air free of pathogens, which they do by exchanging the air in passenger cabins every three to four minutes and passing the circulated air through high-efficiency particulate-arresting (HEPA) filters designed to filter out all particles larger than 0.3 µm by 1 µm.

Comments (153)

  • Kay says:

    However, most of airlines will want to impose more strict measure, masks especially, temperature check (people obviously sick not traveling.)
    Saying that empty middle seat (in addition to mask or other measure) is possibly not reassuring is speculative at best.
    It is an interesting article but barely useful without pointing out what will be different in the futur of travel.

    • Rhys says:

      I don’t think anyone really knows what the future of travel will be like.

      • TGLoyalty says:

        Conference yesterday had the answers on why why we still allow flights and no one is being tested.

        It’s an ineffective way of keeping it out because you test them when they enter but they can pick it up travel test negative at port of entry but See symptoms/ spreading it the next day instead.

        There’s already a large number of people with it in the uk stopping people flying would stop a minuscule amount of new infections.

        • Nick_C says:

          At the daily press conference yesterday, JVT was saying screening on arrival wouldn’t be effective currently, not least because the virus is widespread in the community.

          But he didn’t rule anything out for the future.

          If we could eliminate the current outbreak in the UK, then future travel could mean zoning airports. People arriving from a high risk country should go into quarantine at a secure facility for 14 days. People arriving from low risk countries should should at the very least have satisfactory documentation showing they have been vaccinated, and have antibodies immediately prior to travelling.

          • TGLoyalty says:

            We won’t eliminate the virus from the UK it’ll be managed.

            With all of this stuff it’s not that stopping one transmission isnt potentially a good thing it’s if the measures put in to stop that transmission are appropriate. Does stopping one person passing it on outweigh the human and financial cost of the implementation and execution? Is the solution worse than the problem.

  • Chrisasaurus says:

    Certifiainly makes sense to be sat further back in terms of avoiding infection, maybe AA upgrades will become less hard to find…

    Definitely worth having a discussion around banning the practice of licking the bread to choose which roll to take with your meal, maybe that’s something we should discourage these days

    • riku2 says:

      happily I have never seen anybody licking the bread to decide which one to take but BA and other airlines were handing out a bread basket and letting pax take with their own hands. Some airlines have the flight attendant use tongs to take the bread which is better. Same goes for the unwrapped biscuits in the jar like in the BA lounges (and somebody will no doubt comment that you anyway contaminate the biscuit when you eat it – not aware that you can use a napkin to hold sandwiches and biscuits and not touch food you eat with your own hands).
      The number of times i’ve seen people on planes and public transport eat sandwiches holding them with bare hands and then lick their fingers at the end! No wonder so many people are infected.

      • TGLoyalty says:

        And how many don’t have anything wrong with them at all afterwards?

        I’ll argue that my hand on the piece of bread/biscuit I want is better than me touching some filthy tong that hasn’t been replaced / washed for hours.

        Tbf I pick up sandwiches with tongs as they are always packed tightly and it’s near enough impossible to get one with your hands unless there are only a few left.

        I also worry infinitely more about those people that pick things up (tongs or hands) sniff them then put them back, that’s disgusting.

    • Charlieface says:

      Order kosher, it’s all double wrapped including the bread

  • J says:

    I would think compulsory masks and temperature checks on every passenger might be of a bit more use than blocking out the middle seat.

    • TGLoyalty says:

      Since it can be spread by someone who has no symptoms what use is the temp check.

      The face mask debate continues. If you are unwell you should be at home if you don’t feel unwell (asymptomatic) what’s the real risk of you sneezing or coughing to spread something vs wearing a face mask which can actually cause you to catch something if not handled properly.

      • Cat says:

        Every transmission stopped is a life potentially saved. Some transmissions are from someone who is asymptomatic, some are from those who are symptomatic. No one transmission avoidance measure is the answer, it’s a combination of them all, but yes, temperature and health checks before getting on the aircraft and when disembarking would help.

      • J says:

        The face mask “debate” only seems to be in a few Western countries – and I think for the UK, the advice is motivated more by the fact that they don’t have enough masks.

        • TGLoyalty says:

          I would love to see the actual mathematical data on how many infections people think it will actually stop.

          Poor face masks are as worse than no face mask. False senses of security, spreading from infected cloth to yourself etc

          These debates are as important for any airborne infectious diseases as for COVID19 so I’ll await the output from yesterday SAGE meeting.

          • J says:

            @Cat – Interesting, but I didn’t read anything there about symptomless carriers. Given everyone with symptoms is housebound, I can’t see what information we can take from it. Surely by definition, symptomless means you aren’t coughing at people? Can you explain what I’m missing? 🙂

          • Lady London says:

            Face masks have to be washed by an abrasive method eg a washing machine, after one use at 60 for about 30mins or 90 for about 20min I think and any filter or kitchen paper in them disposed and renewed each use as well.

            Otherwise they are rapidly worse than nothing if not disposable.

          • Cat says:

            Yes J, but you still exhale, and speak, and clear your throat, and cough if you have a common cold and all of those can send out aerosols, many of which will be stopped by a basic bit of fabric. Another method of asymptomatic transmission is lapses of basic hand hygiene which, if you’re used to wearing a mask and do it properly, can be minimised by your nose and mouth being covered and inaccessible.

          • J says:

            Thanks Cat, but my point was that this study showed no cases of the virus present in aerosols (albeit with a tiny sample: n=4) in symptomless carriers. So I didn’t get how this could be presented as “The Maths” to show the effect it would have in lock down Britain where anyone with a cough isn’t allowed to leave the house. I’m not saying masks aren’t worth taking the gamble on, but, even with the new studies coming from Wuhan, the evidence very much is not there yet to show they will help.

        • Andrew says:

          Many from Asia wore masks when travelling even at the best of times so it’s not really a surprise they’re popular there. In the west widespread mask wearing is something you’d expect to see in a disaster movie. I don’t expect it to take off unless it becomes law or there’s very good evidence as to their efficacy.

      • J says:

        “Since it can be spread by someone who has no symptoms what use is the temp check” – Er, because those who do have symptoms are likely to be contagious…

  • Qfx says:

    Back to Easyjet, and leaving the middle seat free; how does that help when someone coughs straight ahead towards the person sat in the row in front of them? Social distancing will go on all year, into the winter, and into next spring. The advice is a 2m radius, not 2m to the side.

    Or when someone walks up and down the aisle and coughs along the way, touches the headrests to steady themselves.

    So sat in the back row may seem a good idea, but thats where the toilets are, where the galley is, so there will be a lot of people walking up and down and standing in that area.

    They may eventually have to enforce wearing masks, which wont work too well when eating or drinking. Then there will be the drunk who decides not to wear a mask.

    In summary, just leaving the middle seat free wont protect anyone.

    • Andrew says:

      It’s purely a PR thing. Watch the policy be reversed as soon as Easyjet can reliably fill more than 2/3 of their planes.

  • mark2 says:

    From a position of ignorance, I assume that the ventilation system of the aircraft will spread any viruses evenly through all cabins. Am I wrong?

    • Rhys says:

      On newer aircraft the cabin air is renewed every 2-3 minutes, and the HEPA filters do a good job of filtering out bacteria and viruses.

      • Cat says:

        It is worth pointing out that coronavirus particles are spheres of diameter 0.06 – 0.14µm. Some aerosol particles carrying the virus will be small enough to pass through those filters.

        • Rhys says:

          Always good to have a mathematician around 😉

        • Polly says:

          Then we can’t stress enough the importance of coughing or sneezing into the elbow. Masks won’t help there.
          Was quite worried on our MAS flt to Bali end of Jan, had to actually ask the relative of a coughing elderly lady to insist on her using one of her many scarves to cover her mouth and nose. It was very unnerving to be near her, across the aisle but too near for comfort. We did wear masks but knew it was useless with that going on nearby. Even with J spacing it wasn’t reassuring.

          Was just feeling the tiniest bit positive about flying until you threw in that stat Cat!

          • Cat says:

            Yes, as Alex M reiterates below Polly – some will get through, some won’t. Every measure that’s taken reduces the risk. Risk isn’t binary – whether you actually catch the virus is, but the probability that you catch it will vary continuously between 0 and 1, depending on the situation and mitigating factors. The index patient wearing a mask lowers the probability, as does the non-infected person wearing a mask sitting nearby, as do the filters in the aircraft ventilation system, as does dab-sneezing (into your elbow, for anyone unfamiliar with that particular dance craze), as does washing hands regularly and thoroughly, and sanitising them when this is not possible, etc.
            Sorry, I turn everything into Maths.
            Occupational hazard.
            Before anyone says it, yes I bet I am fun to be around at parties.
            Polly – keep booking flights, just make sure everything is refundable/using miles, then assess the risk nearer the time. X

        • Alex M says:

          Key word here is Some. Yes, you can’t filter all the droplets carrying virus but you reduce the spread significantly.

        • Qfx says:

          There is a lot more to it than the size of the virus sphere, this was discussed in an article that claimed masks don’t work, which in turn was proven wrong when compared to lab trials. You have to consider the size of the aerosol droplet which carries the virus, the amount of flow and the efficiency of the filter being used.

          Aerosol droplets have a wide range of particle sizes from 0.1 to 900 microns, so both masks and HEPA filters do offer protection but not guaranteed for particles sizes below 0.6 microns (FFP3) or 0.3 microns (HEPA), but a NASA trial showed HEPA filtration is achieved to 0.1 micron – perhaps manufacturers cant or wont guarantee it. Also need to take account of filtration efficiencies, a surgical mask does offer protection, but not 100%.

        • Qfx says:

          Just to add to the debate (confusion), where are those filters on a plane? Does that mean they will be drawing in untreated air past my head? Unless they are in the floor, probably so.

  • SWWT says:

    A very informative study which to me demonstrates that flying is just too dangerous while this virus is around. And the vast (maybe, maybe not, stats mixed on this one..) majority of us do not yet have antibodies so are vulnerable.
    Actually, just walking around where there are other people is dangerous. The 2m rule is a basic and very blunt instrument for prevention of spread. An eminent virologist put it thus (here paraphrased):
    ‘It’s not the droplets, its the aerosol we need to be mindful of. And aerosol carries a long way. When you go into a department store and smell the perfume being displayed three aisles away, that’s the aerosol.’
    Most of us have to go out every once and a while, but when we do we ought to be mindful that the 2m rule is a pretty basic measure.

    • Relaxo says:

      Except…. transmission via droplet is the only proven transmission method. Current evidence actually suggests covid transmission via aerosol is relatively weak. Transmission risk via contact (e.g. food packaging) is even lower.

      • Peter K says:

        You say that, but the fact the whistleblowing ophthalmologist in China caught it, and that was very likely from an aerosoling technique, suggests aerosol contagion is a risk.

        • Relaxo says:

          Relatively weak should not be misinterpreted as ‘not possible’. There are many different plausible interventions to reduce transmission risk, but spending millions on something or drastically changing behaviours to reduce your risk by 1% is pointless.

          • Relaxo says:

            Btw 1% was just an example. Not saying that is the risk via aerosol….

    • Lady London says:

      I do not know why people are assuming having had it necessarily gives any immunity at all. Ditto unsure about how much we can rely on a few antibodies someone have, to derive any useful information yet.

      • memesweeper says:

        So many unknowns! I’m remaining positive in outlook: the infection rate could be very high and immunity easily acquired. We don’t know differently yet.

        • No lockdown for moi says:

          We know it doesn’t kill or badly affect many people under 45

          • Cat says:

            Unless they’re regularly exposed to a high viral load (like doctors, nurses, midwives, paramedics…).

        • Rob says:

          We do. Enough tests have been globally now to show that even in areas of high infection, only around 6% have antibodies.

          • Lady London says:

            Oh dear. Not good then.
            Does that mean there’s not much immunity to this thing left behind in populations. This could be really nasty.

          • Cat says:


  • Nige says:

    Given that an older man is quite likely to visit the toilet with some regularity, isn’t this seat map as likely to show which people went to the loo after the old man as it is the pattern of spread in the air?

    • Cat says:

      …or people who touched the same headrest as the index patient did when disembarking the aircraft, after he had coughed into his hand.

      • The Original David says:

        I’ve always struggled to understand this headrest theory (that it’s one of the dirtiest places on an aircraft). Who actually walks down the aisle grabbing every headrest as they go? I’m perfectly capable of walking in a straight line without holding onto anything when the aircraft is parked at the gate. Very occasionally I’ll need to touch something if I’m walking in the aisle during the flight and there’s some turbulence, but it’s always the overhead lockers I’d reach for, not a headrest, mainly because I don’t want to touch anyone’s head.

        Am I exceptionally agile, or is this headrest theory total rubbish?

        • Peter K says:

          Some questions maybe you’ve not thought of that others have to and so hold chairs/headrests. Not having a go, just something you may not have thought of:

          Am I unsteady on my feet?
          Am I shorter than average and so not tall enough to balance myself using the overhead lockers?
          A youth (see last point)?
          Or have arthritis in my shoulders preventing full arm movement?
          Have I ever had to squeeze past someone in the narrow aisles and was put off balance as I do so?
          Have I ever had to steady myself to put luggage into/remove it from the overhead locker?
          Have I even thought about how dirty the headrests are so know to avoid them?

        • Nick_C says:

          When i used to travel in economy, I found people behind me would grab my headrest for support as they got up and moved out their seat (instead of turning around and using their own seat for support).

          • Jon says:

            Same here. I never really understood why people grabbed the headrest in front rather than pushing themselves up from their own armrests – surely the latter would be more effective, as well as more considerate to the person in front? Sadly I suspect the answer is simply that most people don’t think of anyone other than themselves (or just don’t think) 😉

        • Lady London says:

          You are agile and fit. I never take an aisle seat willingly on long haul. Because 98% if people passing in the aisle yank my headrest to pull themselves along. Not just when the aisle may be sloping. It gets really tedious.

          And most people seem to yank the headrest in front to pull themselves up out of their seat every time they get up these days. I never do but as an ex-dancer I try to keep some middle tone and avoid this. With today’s small seat pitch though, I really don’t blame most people if they do this.

          No wonder the headrests are full of bugs. I shampoo after every flight.

          • Cat says:

            I hate it! As a non-driver, I do the same on trains. People grab for headrests all the time while trying to propel themselves towards the toilet, so you can always find me in the window seat.
            You used to be a dancer LL?
            When this is all over, I vote that the next HfP party is somewhere with a dancefloor!

          • Lady London says:

            @Cat yes I was a talentless dancer but I did quite well thanks to my partner. The skills I have retained from that include getting up out of an airline seat “no hands”, the ability to stay upright for longer during turbulence without grabbing people’s headrests and the ability to spoon on tons of makeup quickly when arriving late. For a party piece I can fix false eyelashes perfectly when driving along even bumpy roads in about 30 seconds when really late.

          • Cat says:

            😂 In 30 seconds? Wow, that’s skill!

  • Nick_C says:

    Getting back to EasyJet, an empty seat next to you is meaningless. Social distancing is 78″. EJ, I would guess, has a seat pitch of 30″ and seat width of about 18“.

    To achieve two metre separation, you would need to allocate the A and F seats every three rows and fly at 11pc capacity.

    But of course EJ is a leisure carrier, and many passengers will be members of the same household. So maybe up to 30pc capacity.

    But I hope no one thinks one spare seat next to you is any safer.

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