That's a good question.
Again, as Dr. Bogoch said, I would be happy to fly at this point, recognizing the other features. The biggest risk factor to flying right now is your destination, particularly knowing what's happening in other parts of the world, rather than necessarily the flight experience and being mindful of the other parts.
That Department of Defense study was interesting because it kept talking about fluorescent particles and that measurement, the filtration and the amount of time they stayed in the air to a detectable quantity. It was about six minutes or two air exchanges.
If you take that on a probability map then, yes, the longer you're on a flight and beside someone who is actively infectious, the longer you may start seeing that exposure. As their burden and their shedding keeps going and going, the air exchanges keep going and going.
The DoD study suggested 54 hours beside a contagious person. I think it is probably dependent on the viral load of the person, the context, how close you are to them, if they're masked or not masked and that type of thing. Certainly, there is a dose relationship. Shorter flights are probably less risky than longer flights where you just have more particle exposure, even with the air exchanges.