Thank you, everyone, and thanks for inviting me here today. I will say that Dr. Bogoch stole a bit of the thunder here, so I'm going to follow up with a couple of points, really focusing on some of the infection control implications of flying, to expand on a couple of Isaac's points.
As Dr. Bogoch mentioned, airplanes seem like a terrible idea. They're hollow tubes in which people are stuck together for a significant amount of time, but airplanes do have a specific ventilation system that is incredibly efficient. Air travels up from the ceiling, down around passengers and down through the floor in a laminar direction. It's mixed with external air. There are HEPA filters and there's an air exchange every two to three minutes. To compare that to typical settings, a typical household setting has two to three air exchanges per hour. Most hospitals aim for 15 to 20 air exchanges per hour, so this is in the ballpark of what would be in an operating room in terms of the air exchanges, air filtration and mixing with external air.
It does show in multiple studies. There was a large study done by the Department of Defense in the United States in which they essentially had mannequins with fluorescent tagged aerosols that were kind of spewing out on the flight. There were sensors set up around all the mannequins. They repeated the experiment 300 times in different positions along the plane. It was a Boeing, a typical jumbo jet, and essentially we saw 99.99% of the particles filtered. They lasted in the environment and in any detectable quantity for six minutes, which is again extremely remarkable and is considered to be in line with what we would expect in health care settings.
Add to that that we still have these universal controls on airplanes in terms of masking and other screening, and some airlines even require testing as part of their entry criteria. There are a number of different things that make air travel relatively safe.
I will speak from my real-world experience. I work at McMaster. We've done an interesting study of airline travellers coming off an Air Canada flight at Pearson where they were invited to self-directed nasal and oral testing as part of their epidemiology look. About 0.7% were positive on entry. A good number of those were actually probably people who had acquired it at their location, likely had cleared and had travelled, but there are a significant number, probably in the 0.5% range, that are actually truly infectious on those flights.
Considering that, if you had a flight of 200 individuals, which is not that dissimilar to what you would have on some of the large aircraft, you would have one person per flight who was positive. We see so many exposure notices out there. In the literature there are a couple of dozen case reports of people who truly acquired it on flights, particularly in that early part where we weren't masking, where things were still uncontrolled, and where people weren't necessarily getting it from their destination. Their only exposure would be on the flight. There were very few cases documented in that sense. It really is a good proof of principle that the flying experience is relatively safe given all the controls and the ventilation associated with it.
These studies are very hard to perform now, clearly, because we have such global transmission. If I get on a flight in India and end up in Canada positive, is it from being in India? Is it from being on the flight? It's very hard to detect now because of the global penetrance of this disease.
That really is my two cents' worth. I think from the infection control standpoint, flights are relatively safe, as long as these controls are in place. There's good experimental evidence to suggest that everything in place to go on a flight, as Dr. Bogoch mentioned, everything prior to the flight and everything after the flight, presents a probably much higher risk than the actual flight itself does, as long as the ventilation systems are working.
I think this is going to be part of the safety plan for opening up flying going forward, being transparent about this type of information, particularly with regard to conveying the risks. We're hearing exposure notifications every day for flights into and out of Canada, as well as for regional flights, and when we really put that into a context of the number of travellers who have truly tested positive, their attribution is truly secondary to the flight, which is fairly minimal considering the global literature around global flying even during the pandemic.