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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)

  • Harry T says:

    Great article. The NEJM is usually brilliant, also.

  • Danny says:

    You really need to correct that headline which says “22 deaths”, when the text makes clear you are actually talking about 5.

    • Dave says:

      A lot of headlines here seem more to get clicks than reflect accuracy. That’s my only real criticism of the site. Of course the last few months there’s been not much in the way of frequent flyer news so they’ve had to scrape the barrel for articles but I hope things pick up after the pussycat virus goes away

  • Nick G says:

    Where’s the 22 deaths then?

  • Al says:

    Swiss are currently leaving every other seat empty. It might be false sense of security but I took it! Sadly needed to take s flight from Zurich to LHR Sunday.

  • Mike says:

    That infamous flight to Vietnam with an “Instagram influencer” on it that was a major spreader of coronavirus should also be investigated…

  • ankomonkey says:

    Maybe the super spreader was a mile-high club veteran, and that’s how it got spread to different parts of the cabin. They might have been prolific on that 3 hour flight!

  • mr_jetlag says:

    good article, as others have said maybe edit the headline… and definitely won’t be showing this to my wife before our June 19th flight (fingers crossed)

  • TripRep says:

    CV19 could spread further than the 2m guidelines we’ve been told.

    https://www.scmp.com/news/china/science/article/3074351/coronavirus-can-travel-twice-far-official-safe-distance-and-stay

    Given that asymptomatic transmission could be as prevalent as those with symptoms I wonder if Airlines will get anywhere near the pax they need for a flight to be economical. This is why the Gov needs to be careful bailing out airlines.

    How many HFP folks want to wear a mask for 10 hours in CW?

    • Relaxo says:

      These are largely theoretical considerations, much like Covid living for X days on a surface. Presence does not imply certain infection

    • Polly says:

      Well, we did, and many around us did on QR back from HKT to ARN end of Feb. Only 6 hr sectors tho. And on MAS from DPS most wore them. Just took them off to eat. And slept with them on too. Think people feel they protect them from small particles to some degree. That, and cleaning all round our seats with set too wipes. But yes, we are anxious about future LH and even SH travel.

      Gov don’t want to promote wearing masks as they f…Ed up with their procurement process, so not enough supplies for the NHS and care homes now. Selling like hot cakes online tho.

      • Nick_C says:

        The WHO is not advising wearing masks, as they say there are no proven benefits. Wearing a mask makes you more likely to touch your face. It will give some people a false sense of security. It is unlikely to prevent you getting infected, although it may prevent you infecting other people. The Japanese wear masks as a courtesy to others, not to self protect. Home made masks will protect others almost as well as medical grade masks, which should be reserved for health workers, carers, and people who cannot avoid close proximity with others in their day to day work.

        If you are serious risk of infection, it is very important to remove the mask properly, from the back, not touching the mask itself. Unlike the Japanese PM on TV recently!

        And look carefully at the reviews if you are thinking of buying masks on Amazon!