IIn the latest guidelines on air travel, the U.S. Centers for Disease Control and Prevention determined that flying domestically is safe for those who are fully vaccinated. However, questions remain about the risks for those who are not vaccinated. Studies have shown that actual flight is relatively low-risk – even without a mask, infectious droplets are unlikely to spread over a few rows – but many flying-related behaviors, from security checks to boarding and disembarking a plane, can add exposure to potential infection.
The VIPRA (Viral Infection Propagation Through Air-Travel) project brings together scientists from different fields to model and analyze these different behaviors and potential strategies for reducing the risks they pose Royal Society Open Sciencethey burden the entry process.
The scientist spoke to Ashok Srinivasan of VIPRA, a computer scientist at the University of West Florida, about the team’s findings.
Ashok Srinivasan: Well, we know for sure that it’s not as high as people think it is. On the other hand, it’s not as low as the aviation industry is trying to make it sound like. A big problem here is that there really isn’t any good contact tracing for people who actually flew in the air. So we really don’t have very good information about what is actually happening. We have papers that people have published, but most of the incidents are not recorded in papers. So you see a lot of cases where there are some overarching events, a lot of people got sick, but this is not a typical situation. . . .
The air that comes out of the plane is quite pure, so it doesn’t infect you, it infects you before the air has passed through the filtration system. And [the filtered air] is much cleaner than restaurants and so on, so the risk of infection from air travel is not as high as in many other places. But of course you packed up a lot of people. . . . because [there are] Large numbers of flights and large numbers of travelers, while the likelihood of infection is small, you will have some large outbreaks.
HOW: So it looks like the boarding process adds about twenty to twenty-five percent to the number of cases. . . . We also compared boarding to moving in-flight, going to the bathroom and all that, and boarding is a much greater risk. Deplaning isn’t as risky as boarding either. Aside from having people sitting next to someone who is actually infected, the biggest risk actually comes from the boarding process, rather than the other aspects of the flight.
The risk of infection from air travel or other situations can be almost eliminated by using an N95 mask or an equivalent mask, so that it can really be very safe.
HOW: We looked at many options. . . . In the paper itself, we only described four different processes because there were too many to report, but these are the most revealing. One is random boarding, which is like having only one zone. The other had six zones plus business class, with entry into business class being the top priority. And then we said back to front and back to front with business class boarding first. And then we looked at variations on it where the center seat was empty, there was no overhead bin, and the windows in front of the aisle were paneled.
HOW: The best thing is random boarding – just one zone. And, of course, among the variations on it, it is much better if you leave the middle seat empty. And if you don’t allow luggage storage, that’s much better. Getting on board before the aisle is much better. These are good for all boarding processes.
HOW: That is partly why. There are two main mechanisms by which the disease spreads. One is when you have people sitting close together for a long time. . . . If the entry process is slow, they’ll sit together longer. So that’s one aspect. The other aspect is, when they actually sit for a long time, they are sitting close together. From back to front, they have to sit close together. If you have random boarding they are scattered all over the place.
The other [primary mechanism] When someone is storing luggage, people usually have to wait to clear the path before they can get on. So when you have more zones people tend to have large groups in some places. If you get in by chance, you’ll have small clusters in many places. And the number of interactions in a small space is roughly the square of the number of people. So it is better to have many small clusters than a few large clusters.
They looked at the most insignificant mechanism and tried to minimize it, and they succeeded.
HOW: They actually changed the procedures to increase the risk. This comes from the CDC guidelines so they have an apology. The reason is that there are three mechanisms by which spread occurs. You are focusing on one mechanism: if people walk past someone who is sitting, what is the risk of it? However, it turns out that the exposure is very low. So they looked at the most insignificant mechanism and tried to minimize it, and they succeeded. . . . That is why the procedure they changed was actually worse than what they had before and much worse than a random procedure.
HOW: Well, so this is a paper; We actually sent it for review about a year ago so the review process was very, very slow. We’ve actually done other work now. And I really think that the risk of infection from air travel or other situations can be almost eliminated by using an N95 mask or equivalent, so it can really be very safe. The most important thing is to actually have an N95 mask and not remove it to eat food and all that on the plane. . . . If people can avoid stashing in the overhead bins I think that would be a good thing. On the other hand, most of it doesn’t matter when people are wearing N95 masks.