Quantifying the Incredibly Unlikely Aerosol Transmission of COVID on Airplanes

Safety/Security, United

There’s a good chance you know someone who has told you, “oh yeah, I know someone who got COVID on an airplane.” That’s most likely not true. Not only is it unlikely that someone could pinpoint transmission like that in the US, but there’s also been plenty of work done showing that it’s probably not happening even remotely often. Studies on transmission via droplets show that masks are very effective at preventing transmission, but what about smaller particles allowing aerosol transmission? We have a new study which gets to that point. The chance of you getting COVID via aerosol transmission on an airplane is remarkably tiny.

The study, thrillingly called TRANSCOM/AMC Commercial Aircraft Cabin Aerosol Dispersion Tests, was commissioned by the federal government in order to test how safe troops would be during transit on commercial aircraft. It’s a worthwhile read, but if you don’t speak science, it might be somewhat… dense. Fortunately, I was able to connect with co-authors David Silcott from S3i, LLC and Sean Kinahan from the National Strategic Research Institute to get my questions answered.

First, let’s get this out of the way. The research was funded entirely by the government. United donated a 777-200 and 767-300 for 8 days of testing, but that’s it. Those aircraft presumably were chosen because they were lying around at Dulles with nothing else to do, but I don’t know that for sure. They are also likely troop transporters, so they are good airplanes to use for this purpose. While David and Sean were highly complimentary of United’s cooperativeness, they made it clear that United had no input in anything except for ensuring the safety of the aircraft.

The Set Up

During those 8 days at the end of August, they did over 800 tests in multiple configurations. Two days per aircraft were spent in the hangar as well as attached to a jet bridge to simulate boarding and deplaning. The other two days per aircraft were spent at altitude.

There were only a handful of researchers in the cabin, but they had a whole lot of instrumentation. Here’s how it looked:

Image via United Airlines

What you see is 42 sensors strapped into seats along with a tape substance on surfaces… all surrounding Ruth. Who is Ruth? Well, that’s the biblically-inpsired name — as in “book of” — given by people at a church where they were doing some testing to the disembodied mannequin with the vacant stare who was patient zero. Here she is looking rather like a guest star on Futurama.

Image via United Airlines

Bad news for Ruth… she was sick with COVID. But fortunately for her, she was also asymptomatic. The assumption was that someone with symptoms would not be allowed to board the aircraft. (Remember, we’re talking about troops here, so the likelihood of someone traveling and hiding symptoms is probably pretty low.)

Fixing the Variables

The study looked at a variety of people with other coronaviruses and some with COVID-19 in the hospital to try to determine how Ruth’s sickness would look in aerosol form. They settled on the two most common sizes of particles: 1 micron and 3 microns. Aerosols can come in other sizes, but these were the most likely to match reality.

The 1 micron particles were given an ultra-bright fluoresence that was easily detectable by these specialized sensors. The sensors would, in real time, measure the particles getting to each seat and then also be able to track dissipation. The 3 micron particles were tagged with a unique string of DNA that would use PCR tests (what the most accurate COVID tests use) to test their presence. A couple tests were done for person to person aerosol transmission with the larger particles, but those were more useful at helping track how they stuck to surfaces.

There were some other tough decisions to make. For example, how much virus would Ruth be shedding? There isn’t a defined science showing that a person will expel x amount of virus. It can vary greatly, but using those sample patients that were measured in other studies, they settled on 4,000 virions per hour. A virion sounds like the latest name for a sports car, but it’s really just a unit of the virus particles.

At the same time, they used 1,000 virions inhaled as being an infectious dose. While there is no silver bullet here, they did say they expect to test out different rates once they get to peer review.

For the tests themselves, they spent a lot of time moving Ruth and her 42 sensor-friends around. On the 767-300, they did a set-up in the front, middle, and aft. On the 777-200, they did the front, mid-front, mid-aft, and aft. Ruth moved around to different seats in each zone so they could measure this from many angles. It sounds exhausting. I hope Ruth was able to lie down and rest when she was up in Polaris.

Oh, and did I mention that Ruth was asymptomatic? I lied. She was mostly asymptomatic, but on the 767, she caught a cough for 30 of the inflight tests. That means the velocity of the particles that came out of her gaping mouth was higher than normal breathing. It didn’t change the particle make-up.

As if we haven’t already talked about enough variables, there were more, including:

  • No mask versus wearing a standard surgical mask
  • Leaving gaspers (air vents) open versus keeping them closed
  • Cabin air system as is with just the 10 people onboard versus with heating blankets over temperature sensors to try to simulate the load on a full airplane and kick the system into high gear
  • Using onboard-generated air on the ground (the APU) versus using ground-provided air

A Positive (or is it Negative?) Result

So, what happened? Not much, frankly, and I mean that in the best possible way. Despite all these different configurations, the results were mostly the same. There was very little aerosol dispersion on the airplane. And why? Well, they confirmed that there were there “dominant protection factors” onboard.

  1. Frequent replacement of air (32 times per hour on the 767 and 35 times on the 777)
  2. Use of a HEPA filter during circulation to weed out particles
  3. The downward flow where air comes in at the top of the cabin and gets sucked out at the bottom

Any airplane that has these features — any modern commercial airplane with more than 50 seats today — will benefit from this. That being said, they only tested widebodies, so could the results be different on a narrowbody? Maybe, but they don’t see why that would be the case. Still, testing would need to be done to confirm.

Digging Into the Numbers

Let’s get into real numbers here. Because of the frequent replacement of the air, the particles in the cabin hung around for less than 6 minutes on average. If this happened in your house, they would hang around for 1.5 hours. When you consider that time is a component of how much virus to you take on, this is a big deal.

You can see full details in the report, but let’s just take a look at the results from a handful of tests on the 767. What you see here is the percent of the virus that was recorded by each sensor when Ruth was sitting in seat 37E at altitude. The three tests in the upper left had her wearing no mask and breathing normally. The three in the upper right had her with a mask, again breathing normally. The four in the bottom left had her coughing with no mask while the four in the bottom right had her coughing with a mask.

The red is Ruth since that’s where 100 percent of the particles start. Keep in mind that the shading is really just meant to give a visual here. That doesn’t mean those people have a chance of being infected or anything like that. It’s just highlighted to show the direction.

What we see here is that in the back of the airplane, the virus particles drifted more toward the back, but we’re still talking tiny numbers here. There is no sensor that recorded more than 0.02 percent of the particles. I should also note that if you look at other test results, those in the front of the plane saw the particles drift more forward while those in the middle saw no favoring either direction. This wasn’t due to seat types or anything like that but just airflow on the aircraft.

For the surfaces, they found that arm rests and table tops collected more than vertical surfaces like seatbacks, but the numbers were still miniscule.

What Does This Mean?

What does this mean for you? Well, they translated that, fortunately. Assuming that you need 1,000 virions to get infected, it would be nearly impossible for you to get sick. The absolute worst outcome they found was in the mid-aft section of the 777. If you had the maximum amount the sensor collected during all the tests — and if no masks were being worn — then you’d have to sit in that seat for 54 hours to get sick. This also assumes that every particle a person expels contains the virus and that every particle that reached the sensor would infect the person. Neither is likely true. Like I said, this is a worst case scenario that still is not very scary.

When you look at the average amount the sensor collected instead of the outlier maximum, nearly all of these would require sitting for 1,000 hours next to someone in order to get sick. The lowest was actually 870 hours. If people are wearing masks, as required, that means aerosols released would reduce by about 90 percent, so you’re talking an even more impossibly high number of hours to get sick.

Limitations of the Study

This is all good news so far, but do keep in mind that no study is perfect. A good study will highlight the limitations, and this is no exception in that regard.

  • This tests only one person having COVID on each flight. If you have multiple people, then chances of infection would increase. But David and Sean noted that there’s no reason to believe that you wouldn’t just add numbers together. The numbers are so small that the chance is still incredibly tiny even with multiple sick people.
  • This hasn’t been tested on a narrowbody, so in theory it could test differently. We don’t know.
  • The numbers showing 4,000 virions being shed per hour and needing 1,000 virions to get sick aren’t fixed in the real world. But considering how low the rate of dispersal is, it can vary significantly and not change the outcome.
  • They did not look at bigger particles which could be expelled especially with coughing or sneezing. Bigger particles have been shown more clearly in other studies to be trapped by masks at higher rates, so that wasn’t the focus.
  • This is about aerosol transmission, not actual even larger droplets. So if someone coughs globs of spittle all over you, or if there is fecal matter sprayed in the lav, those can all end up with different outcomes. Wear a mask.
  • There wasn’t movement in the cabin during these tests. When you go to the lav or the galley, you’re going outside the study parameters. Again, WEAR A MASK.
  • Ruth is stiff. She only stared forward, riveted by that new episode of The Unicorn, or whatever IFE consists of these days with no new movies coming out. Normal people — sorry Ruth, but you aren’t normal — move their heads, turn around, etc so the actual direction of the virus can shift.

The Takeaway

If you’ve stuck it out this long, good for you. Now you’ve reached the payoff. What does this mean for travelers? As long as you’re on an airplane with the three dominant protection factors, it’s exceedingly unlikely that you’ll get sick. Worry more about the rental car shuttle or the airport environment. But that doesn’t mean there aren’t things you can do on the airplane to make it even safer.

I should note that some of these are in the paper, but others are my interpretation based on the study data, so keep that in mind.

  • Use sanitizers to clean the areas around your seat, especially the flat surfaces like arm rests and tray tables with less focus on vertical surfaces. Even if there isn’t much virus at all, it can’t hurt.
  • If you walk around, we know less, so make sure to use your masks (as you must everywhere onboard) and use sanitizer after your return to your seat.
  • Gasp away! There was almost no difference between when people had their air vents on or off.
  • Don’t worry about where you sit. You can’t be sure where a sick person would be in relation to you anyway, and while there were minor differences in where the virus went, it wasn’t much no matter what.
  • Blocked middle seats really don’t seem to matter other than as a marketing exercise. It’s great for travelers to have an empty middle, but there doesn’t appear to be medical reason to actually continue with the practice.
  • Oh, and…wear a mask. I’m a broken record.

I’m traveling on an airplane for the first time since the pandemic began shortly, and I know this study makes me feel a whole lot more comfortable about doing so. The airlines are certainly hoping a whole lot more people feel the same way.

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44 comments on “Quantifying the Incredibly Unlikely Aerosol Transmission of COVID on Airplanes

  1. This is good news. My only small disagreement is on the middle seat. If someone does take off their mask while eating and coughs, if they fall asleep and their head and spittle droop towards your seat, those are potential ways to catch the virus. With a seat between you, this is much less likely. I would still, therefore, prefer a seat between myself and a stranger.

  2. Cranky: this is the reason why we subscribe to your blog. This is a well written, comprehensive, laymen’s explanation of this important study. I, for one, am now feeling more comfortable to be on a plane. I shudder at the “before-and-after” because the crowds at the airport (check-in, security, gate, etc.) are far more scary, far less secure and not researched at all. This is why I am still hesitant to travel (and I used to travel almost every other week for work – it has not resumed yet).

  3. The US airlines owe the US government a big thank you for doing this study; its results are worth far more than billions in additional aid. This study proves that air travel itself does not put one at risk of catching viruses, not just for covid but for virtually all airborne diseases. But the study also highlights the enormous irrationality that is at the root of how covid is being handled and is viewed.
    – Boeing (and presumably Airbus, Bombardier, and Embraer although their jets weren’t tested) knew over 40 years ago (the age of the 767) at least that they needed to address the potential for disease spread on aircraft and they created very capable systems to slow if not stop the spread of airborne pathogens. Covid is not a new thing; airborne diseases existed long before air travel.
    – Despite even the study proving it doesn’t make a difference, UA is touting its program of using APUs to increase air circulation during boarding and deplaning.
    – UA does seem to want to brag on the study to justify not blocking middle seats and, scientifically based on covid; this study shows that seat blocking doesn’t make a difference in the transmission of covid. However, the study didn’t study all forms of disease transmission or factor in the simple preference that most humans have to not be touching someone else that could have any disease and it is inevitable that someone will touch and rebreathe some else’s air when in close proximity. Beyond that, no one wants to be crammed into space if they have the choice of more room and airlines can economically justify offering it. Low load factors right now do justify offering more space right now.
    – Despite numerous studies showing that covid is almost entirely transmitted by air and droplets, there are numerous efforts to use electrostatic spray – but there are significant differences in application from Delta’s practice of every flight to Southwest’s every month. Airplanes are cleaner and that is a good thing but covid might help reduce the transmission of other diseases but all of the deep surface cleaning probably does not change the transmission and infection rates for covid.
    – Even though he is touted as America’s most knowledgeable authority on infectious disease, Dr. Fauci just in the past week made statements that Americans should rethink their Thanksgiving plans based on the potential to be exposed to covid on airplanes, in airports and at family gatherings, clearly ignoring or unaware of this study even though the study was done more than a week ago.
    – Few people will remember that Fauci said early on in the virus (the weekend of March 13) that he would be happy if Americans never shook hands again – not until covid is over but NEVER, highlighting that there might really be attempts to permanently reframe American culture at the hands of a single virus and by selective application of science.
    – Given that some have touted the virus as a means to reduce air travel and global emissions, the airline industry and its supporters have to understand the agendas they are fighting and be prepared to get to the heart of those issues.

    The best news is that the TSA screened more than 1 million people on this past Sunday, the highest number of people since the pandemic started. Business travel is slowly returning. More people are returning to the sky because they are making their own informed decisions about the safety of all aspects of travel and many desire to return to as much normalcy in their own lives as they can.

    This study is great news. Thanks for highlighting all of the factors involved, CF. Well done. Airlines need to highlight the study. Hotels need to doing some similar type of study. The real sources of transmission and the statistically proven reasons for transmission, sickness and death need to be highlighted. Air travel is not one of those factors and airlines need to hammer that home over and over and over again.

    1. But until the situation on the ground significantly improves, this is rather pointless. Sars-CoV2 spread rapidly around the world through international travel – not by people getting infected on planes, per se. It was (and is) the movement of infected people to interact with others then allows the virus to persist. I’m just as desperate to get flying again as the majority of people on Brett’s site, but until travel restrictions are removed, most of us are going nowhere.

      1. While I agree with you on some points, I disagree on others because of the lack of perspective and balance which has been common in discussing covid.
        The virus spread around the world because the internationally accepted norms of communicating and addressing contagious diseases were violated. Commercial aircraft are the fastest means of carrying people around the globe but all countries in the global community have to responsibly participate in the processes to contain the spread of infectious disease and that simply did not happen with covid. This study proved that covid is not spread on aircraft; infected people may travel on aircraft because of a disregard for global health, not because the aircraft is at fault. Overcoming the failure of a government to abide by global public health guidelines is far different from the fear of getting covid on an aircraft.
        And the lack of balance comes from recognizing that covid is the most tracked and reported disease in the history of humanity; there are many other diseases that have been equally or more contagious and/or more deadly and there are other non-contagious diseases for which there simply is not balance or perspective in measuring and reporting communicability, illness and death. For whatever reason, covid became the rallying cry that has been used to make people aware that there are infectious diseases in the world even though they have been there for centuries.
        People have to make their own assessment of risk regarding every aspect of leaving their home, allowing others into their home, and their interactions with non-family members. Covid has awakened people to the risks of living in a world of communicable diseases and some of the principles that can be learned should be applied in other areas of life. People that cannot learn and apply principles of disease transmission will be paralyzed for life.

        The number of people returning to the skies indicates that many people are able to determine their own risk not just of resuming activity but also of staying at home. That is no different than what takes place with other diseases or other events in life. Covid is an infectious disease and those that fail to realize its danger are as reckless as those that force the shut down of communities in order to prevent the spread of a disease when the WHO has said that the wholesale shutting down of communities does more damage to people than more targeted measures.

        Air travel is safe; where people go when they land is a choice but no destination is so contaminated with covid that illness or death on arrival is a given. People will travel when they are given a choice. No one should worry about getting covid on an airplane – but being with other people exposes anyone to a host of potential issues including violence. People simply need to make the decision about how much they want to venture out into the world and in contact w/ other people. This study just proves they can’t blame aircraft environments for covid spread if they choose to stay home.

        Lord Dima,
        if Fauci or anyone else says that there is a risk of catching covid on an airplane (those are his words) and this study says there is not, then he is not following the science that many want to argue is how this disease should be handled.

        1. “This study proved that covid is not spread on aircraft” – no Tim, that’s not how science works. This study provided evidence that within the conditions that were tested, onboard transmission risk was low. That is not proving that ‘covid is not spread on aircraft’. To paraphrase Einstein, ‘no amount of experiments can prove me right, but a single experiment can prove me wrong’. Have a read of this latest case report published last week, describing a COVID outbreak directly linked to a sparsely occupied flight (probably an A330):
          https://www.eurosurveillance.org/content/10.2807/1560-7917.ES.2020.25.42.2001624#html_fulltext
          I wouldn’t claim that this case report ‘proves’ that COVID is spread on aircraft – but it does provide evidence that in the context of that journey, with the cohort of individuals involved, COVID was transmitted between passengers.

          You complain about ‘the lack of perspective and balance which has been common in discussing covid’ – maybe we all – you included – have a lack of perspective and balance?

    2. Let’s not mix two things together – the only thing this study studied (not proved, given all the assumptions) is transmission (via aerosols, not droplets) while on the airplane.

      Unless you are flying a private 777 with 42 of your friends, this study shouldn’t be used to quantify risk of AIR TRAVEL. It didn’t account for many other air travel (not “being on airplane”) factors:
      – stuck in lines (check-in, TSA, jet bridge) with close proximity to people with less to no adequate filtration system
      – poor ventilation/air movement within some (many?) jet bridges
      – all the idiots taking off their masks when in the gate area to talk on the phone, etc
      – public transit to get to/from airport
      – and I’m sure we can come up with more.

      Faucci is not wrong. Just because you might not have a great chance of catching COVID via AEROSOLS while ON AIRPLANE, it does not address air travel as a whole, especially on busy days such as Thanksgiving and Christmas holiday season.

    3. Cranky – Fascinating post.

      Tim Dunn – I agree that the study was worthwhile, and certianly more than “billions in additional aid”. Taxpayer funds should stop flowing to the airline industry at this point (particularly as public transit is not receivng any aid). New York City’s MTA alone carries more riders per diem than the entire airline industry, and won’t get a “bailout” – if that’s the case, then neither should airlines! As per another blogger:

      *** Pre-covid, the MTA had a daily ridership of 5.5 million people. Last year, the nation’s airlines averaged 2.9 million passengers per day. So far, the privately-held corporations that run the nation’s airlines have received $25 billion in grants along with $35 billion in loans on very generous terms. ***

      And similar studies have shown that transit is simply not a primary vector for COVID transmission, by the way. Just food for thought!

      1. “*** Pre-covid, the MTA had a daily ridership of 5.5 million people. Last year, the nation’s airlines averaged 2.9 million passengers per day. So far, the privately-held corporations that run the nation’s airlines have received $25 billion in grants along with $35 billion in loans on very generous terms. ***”

        “And similar studies have shown that transit is simply not a primary vector for COVID transmission, by the way. Just food for thought!”

        I think you are referencing the APTA study that came out recently stating that transit doesn’t cause Corona to spread. It was in defense of a falsehood spread by a poorly developed study at Harvard. As a result, the transit industry may have been forever injured do to no fault of their own.

  4. Thanks for the summary, Cranky. It’s great to see the empirical confirmation that airplane circulation systems make an enormous difference. My takeaway: the big risk from being on the airplane is the people within 2 m of you transmitting via droplets, especially if any of them aren’t being good about wearing a mask. That means the risk is that one in ?10 people sitting closest to you for a 2+ hour flight are contagious, not that one in ?150 people anywhere on the plane, which obviously significantly reduces the risk.

    Another risk that you allude to is the general public is not likely to be as good as military personnel travelling on orders about refraining from travel if they’re sick. Preventing that seems like a significant sociological challenge.

    Reading the original article, I’m a bit concerned (and surprised) about the lack of a clear control. I’d like to see the numbers for the airplane just sitting still in the hangar with no ventilation, where you would really expect significant risk of transmission based on everything we know about SARS-CoV-19. They have hangar measurements, but they are “simulated inflight hangar” measurements rather than just a baseline. What would be most convincing to me is not seeing the raw numbers but how much the filtration system reduces the prevalence of aerosols compared to a baseline with the filtration system off. Did I miss that somewhere?

    It would be good to see this tested on narrowbody and regional jets. I would think it would be *very* much worth the cost to the airlines to provide a 737 and an E175 to an independent third party for this kind of test to test empirically whether the conclusions from widebodies also apply to smaller planes.

    And of course, as others have noted, travel itself remains dangerous both for the traveller and the people in the communities at both end of their trip as long as the virus is as uncontrolled as it is now in most of the US or even Canada (where I live). Maybe one could safely (from a virus point of view) fly around on an airplane all the time, but if you’re actually going anywhere after you get off the plane, you risk infecting a new population and/or getting infected yourself and bringing it back home, and a single negative test doesn’t mean all that much because of the variable incubation period.

    1. Alex – I don’t believe they tested it with the filtration off since there is no scenario where people are subject to that condition.

      1. As a scientist, that strikes me as really weird. It seems like a natural control. In real science, it’s rare to have as good a control as that would provide, and it would make the experiment *much* more convincing.

        It is a very interesting question; what we really want to know is how the risk of transmission on an airplane compares to the risk in a more normal place. Turning the ventilation off would make an airplane much more like a “normal” moderately-crowded place, which we know is fairly risky. Without that control, I think you’re drawing rather stronger conclusions from this study than the study merits. If I were refereeing this as a research paper, I would definitely send it back and ask them to do the control experiment (or at least justify why they didn’t).

        That said, I generally agree that it seems most likely that with the good ventilation, an airplane is not nearly as risky as one might assume by comparing it to a crowded restaurant. It’s a shame this didn’t do (or show?) the simple extra experiment to nail that down.

        1. Alex,
          there are few public buildings in the US and Canada that have no system of mechanical ventilation so still air is not the norm.
          Most medium to large buildings in the US have fan-forced ventilation and many buildings have improved air filtration systems as a result of covid. Some houses and older small public buildings have radiant heat but that is much less normal in large buildings and it doesn’t exist in transportation systems (trains, planes, buses). Covid might force public building operators that use radiant heat to add filtration systems.

          But let’s once again be clear that covid is not the first airborne disease the modern world has faced; it might be the impetus for companies including airlines to do things to limit the spread of pathogens but if those things were needed, reduced covid counts are not the only positive outcome.

          Many of us have been on an airplane without air moving at all – and that isn’t pleasant for many reasons and most responsible airlines have long avoided it by using ground air or an APU.

          The world has figured out how to identify covid risk, identify infected people, and treat those that are sick from it and hopefully soon vaccinate people. People still get sick and die from the flu even though there are vaccines. We won’t eliminate covid but like other diseases, it might die off.

          As humans we can identify problems and minimize risk through some pretty incredible technology and our ability to adapt continues to improve; we can’t eliminate all risk for anything.

          Airborne diseases aren’t going away. People have to decide when they are ready to venture back out in the world and their decision – including the economic consequences – need to be respected.

          The notion that airplane cabins are airborne disease spreaders needs to come to an end. Public health officials and everyone else needs to recognize that technology addressed this problem decades ago before covid ever became a thing.

          1. Tim,

            It seems to me like you have a bit of an axe to grind here. Of course COVID-19 is not the first airborne disease. However, by looking at excess mortality statistics, it’s pretty clear that given the current standard of care, it has an uncommonly deadly combination of infectiousness and case mortality rate (a somewhat low case mortality rate being part of the deadliness since it facilitates transmission), and it has transmitted enormously effectively in indoor settings despite (or possibly even because of) the ventilation systems you refer to. Some combination of a) vaccines which (like the flu vaccine) both reduce the prevalence in the community and reduce the severity of cases for vaccinated people who get it and b) improved standards of care as the medical professionals learn more about the disease are likely to make it much less dangerous over time (and hopefully that timeframe will be months, not years), but we are not there yet.

            I was not arguing that airplanes are places where SARS-CoV-2 transmission is high. I was instead arguing that without a control, this study doesn’t demonstrate that transmission is low as effectively as I would like. It strikes me as really weird to not have that obvious-to-me control as part of the experiment.

            1. Alex
              I enjoy the interaction.
              The CDC itself has said that the mortality rate for covid vs. the flu is not any different for seniors.
              The CDC has repeatedly said that well-ventilated rooms help reduce virus transmission.

              covid is ALREADY much less fatal than it was initially. Remember all the talk about the need for ventilators? now, doctors know that intubating too early can actually lead to higher rates of death.
              Steroids are being used to reduce the inflammation process and the strategies are working for many people.

              Remember this is all happening w/ no vaccine. There is a flu vaccine and yet the death rate for seniors is no different. Your “it will get better in the future but we aren’t there” doesn’t square w/ actual statistics.

              No, I have no axe to grind. I am an analyst. The data simply does not support alot of the decisions that are being made about public health – and, once again, the WHO now says that lockdowns and mass quarantines don’t work and do too much harm w/o addressing the root problem of a rampant virus, no different from what exists w/ other diseases.

              and the reason why there is excess mortality is because so much other activity has been suspended – so people are not getting into accidents at the same rate, not being diagnosed w/ cancer etc. “excess mortality” is not even an accurate measurement without controlling for the decline in other causes of death which any objective scientist knows have not all been reduced – but they are just not being reported as frequently.

              There were controls for the study. CF reported them and they are there for you to see in the full report. You, as a scientist can reproduce the test using more robust conditions but when the study showed virtually no transmission under any scenario, then the notion that the study is flawed doesn’t really work.

              What is needed is for there to be comparable studies in multiple environments to show where disease transmission really does occur. I would strongly bet that it will show that being too close together in poorly ventilated environments (older buildings, small rooms) is the most vulnerable place for someone to be.

              And your point also raises that there are people – even so-called scientists – that are not as driven by data and science as they claim to be.

              I am not doubting Fauci’s knowledge or contributions – but when he says that he wants to never see Americans shake hands again and is ignorant or simply chooses not to include this study in his advice about air travel, he is not objective. I don’t have an axe to grind to note the logical inconsistencies and the lack of application of science.
              I do ask the questions and make the observations that others with biases don’t want to or won’t ask.

              The fact that the number of people traveling by air continues to increase in the US while it is flatlined in parts of the country that have hard quarantines says that the reduction in air travel is as much about the inability of people to freely travel as it is about their fears of becoming infected.

            2. First, *everyone* has biases. The important thing is to try to recognize your biases. The claim that someone is an “analyst” or is looking at data doesn’t make them free of biases.

              The important number isn’t the case mortality rate, it’s the overall mortality rate, which is the product of the case mortality rate and the probability that someone will get infected. *Even with* all the lockdowns and reduced contacts, the overall mortality rate due to COVID-19 is alarmingly high, 1.1 million deaths worldwide compared to 290,000-650,000 deaths from flu in a typical year (without physical distancing, masks, etc). The same public health measures are effective against both the flu and COVID-19, and they have dramatically reduced the rates of both. This is easiest to see in the southern hemisphere, which has now been through a flu season in the COVID era and basically not had a flu season at all, an indication of how effective these measures have been at reducing the impact of respiratory viral diseases. The fact that COVID-19 is *still* as deadly as it has been indicates just how bad it would be without the measures we’ve taken.

              I’m a little baffled at how one can look at, for example, the CDC pneumonia, influenza, and COVID-19 mortality statistics (hopefully this link will work: https://www.cdc.gov/coronavirus/2019-ncov/covid-data/covidview/07032020/nchs-mortality-report.html ) and claim that the CDC is saying that COVID-19 is no more deadly than influenza.

              I agree that we have made considerable progress on combatting COVID. But we’re not to a place where the death rates have made the danger posed by this disease approach acceptable without substantial preventive measures.

              I’m also confused by the claim that the fact that people aren’t dying in car accidents makes the higher overall mortality rates somehow due to the lockdowns and not COVID. Controlling for the reduced “regular” mortality makes the high excess mortality look like more COVID-related deaths, not fewer.

              Where are the controls that Cranky or the original study describe? I read both, and I don’t see them. The study says nothing about transmission; it is about propagation of aerosols. Now it’s very likely that the propagation relates to aerosols, but that’s not what the study covers. One thing I am very aware of as a scientist is that it is crucial to calibrate any measurement. “Virtually no” aerosols is a very difficult thing to quantify without a baseline measurement; I want to know how the airplane environment reduces spread of aerosols (and droplets, which aren’t the subject of this study, which is fine) relative to the kinds of similar-sized environments in which entire large roomfuls of people have been infected by one spreader. The control I ask for is something that would provide that baseline measurement. I don’t see anything like that here.

              As I said, I agree that this study suggests that aerosol propagation is not something to worry about in airplanes. It would just be a lot more convincing if they had a control that shows the situation in which there *would* be significant aerosol propagation; then this study would demonstrate that airplane enviroments are much better than this baseline. I don’t see that here, and that’s too bad.

              Dr. Fauci is an epidemiologist. From an epidemiological point of view, shaking hands is very clearly a bad thing to do, and he’s right to say so even while he recognizes that shaking hands is not likely to go away permanently. He never suggested that it should be a public health order or anything like that; he simply said that we would have a lot less influenza if people didn’t shake hands routinely. He’s probably right. He provided further context shortly after the interview you’re (I presume) referring to: “I mean, I said that, you know, somewhat serious and somewhat realizing that that likely will never happen.”

            3. “I am not doubting Fauci’s knowledge or contributions – but when he says that he wants to never see Americans shake hands again and is ignorant or simply chooses not to include this study in his advice about air travel, he is not objective.”

              That two caught me by surprise when I herd him say those words & made me ponder a few questions on this subject. I assume you know that Fauci washes his hands so often that it averages once every 19 minutes
              per day – I did the math. a bit OCD wouldn’t you say even for a scientist of his calabor?

              I don’t have an axe to grind to note the logical inconsistencies and the lack of application of science.
              ” I do ask the questions and make the observations that others with biases don’t want to or won’t ask.”

              And what biases are those Tim?

            4. Sean
              I don’t assume anyone has biases until they make them apparent. I didn’t know what you just shared about Fauci’s handwashing frequency but he is a northeasterner and he has seen the world enough to know that other cultures do not shake hands or touch like Americans or Latins do.
              Is it potentially safer for Americans and Latins not to touch as much as they do? Perhaps. But to share that bias at the beginning of a period where he has been “knighted” as America’s premier infectious disease expert raises questions about the policies that have been implemented, esp. since covid has been shown to have extraordinarily low TRANSMISSION rates via touch.
              and if Fauci is touted as an expert and either doesn’t know about or ignores the study in this article, then that severely reduces his credibility to talk about risks.
              I personally have liked Dr. Deborah Birx much more as a data scientist and not a politician – and she has a much better leadership personality than just about all of them.
              It is precisely because people on both sides of the issue have significant flaws in the logic they are using to explain their actions that people are beginning to make their own decision and the US and global health care authorities take a reputational hit in the process.
              And without being partisan, there was a huge hit to the reputation of public health authorities regarding changing advice about the travel blockades and mask guidance early in this.
              The reality is that both sides got a lot wrong in the early days of this virus and some are still not evolving their positions to generally accepted global policy.
              I am for science and for data – but data cannot explain everything and science does evolve as we learn more about the world. A little humility and honesty from all those in authority would do wonders but instead we see incessant beating the other side up.

              The connection of all of this to air travel is that those people that are making up their own minds and beginning to travel are doing so based on their understanding of the covid world in which we live.

              to Hov’s comment below, I have flown Southwest and Delta multiple times during the pandemic and have never seen either go above their load factor cap. Delta makes a bigger deal about cleaning and letting you know it but both are doing a good job; Delta just adds more touches like handing everyone a wipe as they board so you can wipe down your own space yourself. I have not been on any other airline and will not as long as the option of extra space is available from at least two of the largest US carriers.

  5. Thank you for the detailed analysis. I have been on over 100 flights since Covid broke out in the states without incident.
    It’s all about common sense. Don’t lick the seats, tongue kiss the stranger next to you, simple stuff like that.

  6. Crankster pulls off another translator masterpiece! Don’t miss this very easy to understand and, appropriately timed, humorous look at a scientific study of covid transmission on airplanes. Well done CF!

  7. Question: does the study somehow address risk when the circulation is off (as sometimes seems to happen) prior to boarding and after arrival? That seems to me to be a major shortcoming of this study, but I might not understand how this was addressed in the study or something about circulation when the plane is not fully powered.

      1. Thanks for the response and the post, I’ve been trying to get more clarity on this. My take away is that this study holds if things go as planned. But, if something goes wrong with ground power or like (as happens with some regularity), then the risk could increase significantly without a great way to minimize or manage it in the moment.

        1. SW – This would have to have a ground power failure and the APU inoperative. I don’t imagine that happens often. But yes, it’s possible.

  8. Of the people reading this blog, I’ll bet most of them yearn for the day when they can get on an airliner and fly off to some magical, or not so magical spot. We hope studies will make us feel safe to take that trip.

    But, those of us who have sat in an economy seat and had their fellow travelers, left and right, quickly snooze off and gravitate into their space. or had the person seated in from of them recline his or her seat all the way back into your lap, knows that even before the pandemic things where not always the best. And, jamming yourself into a regional aircraft seat, same.

    And, how many times have you seen passengers unfasten their seat belts at the very first opportunity, never to buckle up the rest of the flight. My guess is that these are the same people who will make a quick effort to hide the fact that they are not using their face masks correctly, if at all.

    If United, or anyone wants to get me on any of their flights in the immediate future, do some studies showing that they have checked on a selected and significant number of their flights–25, 50, 100 or, whatever is a significant number, and chose a select number of passengers to have themselvee checked for covid-19 on their flight, (1) just before boarding, (2) immediately on disembarking, and (3) a short period time thereafter–5 days, a week, whatever, and let me and the world know what the negative/positive results show.

    I’d be glad to volunteer as a test-traveler. Of course, let the government fund the tests, compensate the passengers for all of their help, inconveniences, and troubles, and have health experts run, manage, and report on the tests and results. The time is ripe to go to these extremes while we have airlines still trying to operate. Anything short of this isn’t going to convince me to fly.

  9. While this study looks pretty exhaustive, we have to be careful with the conclusions. Over the past few decades, we have had real (or at least, suspected) cases where different viruses (SARS, influenza) have spread on commercial aircraft. The most famous was, if I recall correctly, an Alaska combi in 1977, but there have been others. So the results of this experiment need to be considered in light of real world experience, and not in a vacuum.

  10. Exceptionally well-written Cranky. Thank you! I actually have flown numerous times since June and have felt safe (In the airplane; the gate area at some airports is a hot mess, however), focusing all my flying almost exclusively on Southwest Airlines, the only airline guaranteeing empty middle seats (Delta advertises it but has had numerous examples of bait and switch either on small planes or when another flight cancels).
    One point I would submit to you: there actually HAVE been some studies looking at empty middle seats And they have found it DOES reduce your risk even further. Here’s the latest example, though not peer reviewed yet: https://www.medrxiv.org/content/10.1101/2020.07.02.20143826v3

    Thanks again!

  11. There are two major problems with this study: it is extremely technical and therefore difficult to comprehend and assess. The public have to rely on the very positive conclusions without being able to make up their own mind. For that very reason the study is useless to restore confidence of passengers.
    The other problem lies in the fact that the study assumes there is only one sick passenger on board.
    Personally, I do worry when, on a long haul flight, all passengers take their meals at the same time….without wearing a mask. Not to mention undisciplined passengers removing their masks during the flight.
    Therefore I canceled 6 trips already this year. And I am not planning any new trip until I get a serious reassurance.

  12. Cranky,
    With WN cancelling their blocked middle seat policy effective 12/1, it would be interesting if you did an article on “did the safety of a middle seat block create a revenue premium for anyone?”. My quick take on the data is no but I’d love your thoughts.

    1. Mike,
      I hope CF does address your question.
      UAL tried to answer that question in its earnings release when it said it was certain that it would beat its legacy competitors (clearly targeted at American and Delta); their statement clearly is about revenue ratios (RASM) but they underperformed Delta on a number of metrics – such as yield, debt service, and profit, even adjusted for Delta’s refinery.
      American underperformed DL and UA on revenue metrics but that wasn’t a huge surprise.
      United has been the most reluctant to return capacity even on their domestic system – and CF has closely tracked capacity returns.
      For being slow to return capacity, United has seen a rash of competitors add capacity to its markets. Now those competitors could see UA as more vulnerable financially (along with AA) but the more likely reason is that airlines have a list of markets they want to serve and UA’s failure to add capacity makes an easy opening for other carriers to add capacity.

      So, middle seat blocking is only part of the equation. The change in competitive capacity will be another part of the final analysis about whether carrier’s specific strategies worked the best or not.

      1. No one asked you. It wasn’t directed to you. And I didn’t want your opinion.
        Keep your distorted analysis to yourself.

        1. you do realize you are posting on a public forum?

          Tell us, since you are on a public forum and not in a private email (which you could do), what you think will happen?

          Do you really think that share shifts wouldn’t happen if airlines didn’t restore the capacity that other airlines are willing to add?

            1. I affirmed your request that CF take a look at the question you posed.

              And to further expand on what I said above, you can find the answer by looking at financial statements; almost all of the airline industry has now released their 3rd quarter financial results.

              DAL reported the lowest passenger yield decline followed by UAL (fractionally lower than DAL) then AAL and then LUV of the big 4. ALK’s yield decline was better than the big 4.

              There are all kinds of seat blocking strategies in those results – so it is hard for anyone including CF to draw any other conclusions based on currently available financial data.

            2. Just to add, this is CF’s blog and I defer to him on what he chooses to address and his opinion when he posts them.

              He didn’t reply to your comment in the nearly 24 hours that it has been posted very likely because there is no conclusive answer one way or another given that there are not consistent yield change differences between carriers that seat block and those that do not.

              There are clearly other dynamics that are at play in why those yield differences exist.

              I am sorry if I offended you by replying until/if CF decides to do so.

  13. Just a comment about one line in one of Mr. Tim Dunn’s misleading blurbs, where he says “…and if Fauci is touted as an expert and either doesn’t know about or ignores the study in this article, then that severely reduces his credibility to talk about risks.”

    Dr. Fauci was appointed director of NIAID in 1984. He oversees an extensive portfolio of basic and applied research to prevent, diagnose, and treat established infectious diseases such as HIV/AIDS, respiratory infections, diarrheal diseases, tuberculosis and malaria as well as emerging diseases such as Ebola and Zika. NIAID also supports research on transplantation and immune-related illnesses, including autoimmune disorders, asthma and allergies. The NIAID budget for fiscal year 2020 is an estimated $5.9 billion. He also graduated first in his class from Cornell University Medical School.

    So don’t pay too much attention when Dunn says “…if Fauci is touted as an expert…” Dunn is in NO way qualified to opine on Dr Fauci or epidemiology in general. However if Mr. Dunn wants to come back to this comments section after he has managed a $1.1-$5.9 million budget for a research organization for many decades, I’ll pay more attention to his virus opinions.

    1. No one including me has doubted anything you said but it doesn’t change that Fauci has stated that there is a risk of catching covid on a commercial airplane. This study and others show that airplanes are the least likely places to get covid.

      In fact, it is well-documented that the one of the biggest covid risks right now in the US is from social gatherings, esp. indoors, that involve people that are not from the same household and thus at a high risk of introducing pathogens to each other.

      When someone says they are an expert and either doesn’t know about the research that was cited here or specifically ignores it and makes statements that are counter to what this research and multiple state and local officials are saying as well as Dr. Deborah Birx, then red flags do go up.

      If you really are with the NIH, then I appreciate you and your work. I really do. And I appreciate what Dr. Fauci has accomplished in his distinguished career as well. Maybe we have different ideas about leadership, but when I see someone at the top of an organization that involves knowing new information that is coming in on a daily basis, then I expect them not to make statements that counteract research that is publicly available.

      I have flown multiple times during the pandemic, esp. from June forward. There are many places where I put my guard up but a Delta (and for a few more weeks a Southwest) airplane is not one of those places. The science validates that my actions and behavior are rational and based on science.

      I look forward to your comments specifically addressing Fauci’s statements about covid risk on commercial aircraft in light of this study.

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