In its latest guidelines on air travel, the United States Centers for Disease Control and Prevention said flying within the country is safe for fully vaccinated people, but questions remain about the risks for those who do. are not immune. Studies have suggested that actual theft is fairly low risk – even without masks, infectious droplets are unlikely to spread beyond a few rows, for example – but many behaviors associated with theft, security checks upon boarding and disembarking the plane, may increase the potential exposure to infection.

The Viral Infection Propagation Through Air-Travel (VIPRA) project is bringing together scientists from various fields to model and analyze these different behaviors and potential strategies to reduce the risks they pose, and in an article published on April 28 in Royal Society Open Science, they are involved in the boarding process.

The scientist spoke with Ashok Srinivasan of VIPRA, a computer scientist at the University of West Florida, about the team’s findings.

The scientist: What do we know about the risk of catching COVID-19 from traveling by plane?

Ashok Srinivasan: Well, we know for sure that it’s not as high as people think it is. On the other hand, it is not as low as the airline industry is trying to suggest. There’s a big problem here in that there really isn’t a good contact tracing done on the people who actually flew in the air. So we really don’t have very good information on what’s really going on. We have articles that people have published, but most of the incidents are not recorded in the newspapers. So you see a lot of cases where we have a few events spreading, a lot of people got sick, but that’s not a typical situation. . . .

The air coming out of the plane is quite pure, so we don’t get infected because of that, we get infected before the air has passed through the filtration system. And [the filtered air] is much cleaner than what you would find in restaurants and stuff, so the risk of infection from air travel is not as high as in many other places. But, of course, you have a bunch of people packed together. . . . Because [there are] a lot of thefts and a lot of people traveling, even if the probability of infection is low, you are going to have big epidemics.

ST: And to what extent does the boarding process itself contribute to the risks associated with air travel?

LIKE: So it appears that the onboarding process contributes about twenty to twenty-five percent of the number of cases. . . . We also compared boarding versus in-flight movement, going to the bathroom and all that, and boarding is a lot riskier. Disembarking is also not as risky as embarkation. So apart from people sitting next to someone who is actually infected, the biggest risk actually comes from the boarding process, not other aspects of the flight.

The risk of infection from air travel or any other situation can almost be eliminated by using an N95 mask or equivalent, so it can really be very safe.

ST: In your study, what methods of internship did you examine?

LIKE: We looked at many options. . . . In the document itself, we only flagged four different processes because there were too many to report, but these are the most insightful. One is random boarding, which is like having only one zone. The other had six zones plus business class, with business class boarding first. And then we said backwards, and backwards with business class boarding first. And then we looked at variations of these with an empty center seat, no overhead storage compartment, and a window panel before the aisle.

ST: And which one was the best?

LIKE: The best is to have a random boarding, a single zone. And among the variations of that, of course, if you keep the middle seat empty, that’s much better. And if you don’t allow luggage storage, much better. If you go up to the window before the driveway, much better. These are good for all boarding processes.

ST: Is it just because of the boarding speed? I know previous research has shown that windows first and random are faster than back-to-front boarding.

LIKE: This is partly the reason. There are two main mechanisms by which the disease is spread. One is if you have people who sit next to each other for a long time. . . . If the boarding process is slow, they sit together longer. So that’s an aspect. The other aspect is that when they sit for a long time are they sitting close to each other. From back to front, they should be seated close to each other. If you have random boarding, they are spread all over the place.

The other [primary mechanism] This is when someone is storing luggage, people usually have to wait for them to lead the way before they can enter. So if you have more areas then people tend to have large groups in a few places. If you have random boarding, you have small groups in many places. And the number of interactions in a small area is roughly quadratic to the number of people. It is therefore preferable to have several small clusters rather than a few large clusters.

They looked at the most insignificant mechanism and tried to play it down, and they did it.

ST: Are current airline procedures consistent or not with what you have found to reduce the risk of infection?

LIKE: They actually changed the procedures, generally, to increase the risk. This is from the CDC guidelines, so they have an excuse. The reason is that there are three mechanisms by which the spread occurs. They focus on one mechanism: when people walk past someone who is seated, what is the risk that is. But, it turns out that the exposure is very low. So, they looked at the most insignificant mechanism and tried to minimize it, and they got there. . . . This is the reason why the procedure they changed was actually worse than what they had before, and much worse than a random procedure would be.

ST: What other air travel risks would you like to consider that you haven’t had a chance to consider here?

LIKE: Well, so it’s a document; we actually sent it out for review about a year ago, so the review process has been very, very slow. In the meantime, we’ve actually done other work. And, I think, really, the risk of infection from air travel or whatever can almost be 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 to take it off to eat food and all that on the plane. . . . If people can avoid stuffing themselves into the overhead compartments, I think that would be a good thing. On the other hand, if people are wearing N95 masks, then most of it doesn’t matter.

EditorNote from: This interview has been edited for brevity.