Swiss Cheese: or, About That Flight To Florida

In the other day’s article I posed a question: How safe is it for me to fly to Florida over Thanksgiving?

And then I didn’t answer it. Sorry about that; articles should only be just so long, and that one kinda got away from me.

To recap: What you actually need to know are the answers to three questions:
– How likely am I to be exposed to COVID if I’m flying on a plane?
– If I’m exposed on a plane, how likely am I to catch COVID?
– If I catch COVID, how likely is it to be serious?

Roughly speaking, answer each of those questions and multiply the odds together, and that’s the actual risk. Examine it from the perspective of precautions you take (vaccination, wearing a mask, et cetera) and it’s known as the Swiss Cheese risk assessment model; the idea is, any single precaution will have big gaping holes, but add more and varied safeguards and the holes vanish.

For the answer to the third question, the appropriate statistic to look at is the Infectious Fatality Rate, or IFR. That’s the literal answer to the question: If a random person gets infected, how likely are they to die as a result? And serious cases are ten times as likely as death, give or take.

For our purposes, 1.0% is the IFR*. It’s substantially lower if you’ve gotten vaccinated, and if you’re young and extremely healthy it’s lower still — but never zero.

One side note: Just how healthy are you? I’ve known a marathon runner who dropped dead from an aneurysm he never suspected, and at least a dozen people who have some vague ailment that doctors can’t seem to diagnose. Or, take it from another, longer perspective: Everyone’s carrying around at least one cause of death that they don’t know about yet, but will one day discover. So don’t be so quick to dismiss co-morbidities; there but for the grace of God go we all… eventually.

Back to the math.

Let’s say you’re reasonably healthy, and so is your family of four. You all have your shots (yes, the kids too), and you’ll all wear masks. Each one of you has an IFR of around 0.2%, more or less. We’ll presume that if only one of you dies it’s still a bad thing, so that works out to a hair under 0.8% total probability of a negative outcome. Still not very high.

Now we look at the contagious nature of COVID, specifically the Delta variant. It’s airborne, and while masks can reduce spread, it’s still got a base R number of around 6. On a long flight in an enclosed metal tube that uses even medically filtered air (which your plane may not), the odds are increased. Does anyone remove their mask to eat? And what about the airports on either end, the cab ride, the car rental agent, the… Anyway: If any of these people has COVID, you’ve got roughly a 70% chance of being exposed enough to catch it. You might fight it off, sure — but that’s what the other number, the IFR, is for. Now, if all four of you stay together at all times, never go off alone to use the bathroom, and so on, this number doesn’t go up — but that won’t happen. And someone will rub their eyes, and someone will forget their mask, and so on. That’s life; it happens. The industry touts their active ventilation and DOD studies**, but even they only say it’s better than most indoor environments.

The average plane to Florida carries around 200 people, and they’re running nearly full again — unlike at the beginning of the pandemic, when rows were left open. Transmission occurs almost entirely when people are asymptomatic, whether or not they’re vaccinated. So what are the odds that, if you take 200 people at random, none of them have COVID? Somewhere around 45%, right now. And, while you might not bump into the sick one(s) on the plane, and the ventilation might work as advertised, what about the security check and the waiting area in the airport and the bathrooms? Last time I looked, there were very few precautions being taken at airports.

So. Up to .7 for the contagion, times .45 for the plane, times .008 for a family member dying. That’s a 0.25% chance. Only a one in four hundred chance; not too bad, right? Fairly small odds that someone in your immediate family will die if you take a plane to Florida to share Thanksgiving with your family… your elderly, vulnerable family… Don’t you have that one crank uncle who refuses to vaccinate or wear a mask? One in four hundred — that beats Russian roulette all to hell! And you really, really, really want to go.

Almost forgot: The chance of serious illness is ten times the chance of death from COVID. So one in forty. And everyone you dine with on Thanksgiving has the same chance as you of catching it on the flight in, and unless you wear masks at the table… Oh, and the odds multiply, so… Hunh. Sounds like Russian roulette after all.

There are alternatives, mind you, ways to improve the odds so you don’t kill your family; this is where the Swiss Cheese model comes into play. Obviously, if everyone on your plane strictly observes mask safety, and if it’s a short flight, you’re far better off. All things being equal, discount airlines have worse maintenance, and therefore less trustworthy air filters. Don’t travel with small or undisciplined children (that should go without saying, but doesn’t). If you’re worried about other people’s kids, take a sleeper car on Amtrak, where you don’t actually have to hang out with people. Consider wearing goggles to protect your eyes; disinfect; handwash. Maybe just drive to Florida; it’s only… what, fifteen hours? Make sure it’s a small gathering, only a couple of people plus you, and perhaps even have the meal outdoors. It’s Florida; the weather’s fine.

Each precaution you take and every risk factor you reduce improves everyone’s odds. If you’re extremely careful, you could be perfectly safe. As safe as crossing the street, say.

Or maybe just Skype the grandparents again instead of taking a risk of exposing them. How about that?


*NOTE: I’d be happy to show my work extrapolating the IFR if people care enough; I’ve done it before. However, we’re talking about me putting several pages of scribbled math into a post, which would take me at least a couple of days. And the last donation I got for a TNFN article was… maybe July? So, unless you feel like donating, just accept that I’ve done the math, and then I pinned down an expert and asked if I was right. Same goes for the 45% chance of a flight being COVID-free, and the R number versus contagion rate.

** The DOD study used mannequins back in mid-2020. Mannequins, unlike small children, are well known for such things as not scratching their noses or taking off their masks to eat. Of more applicability is this article.

EDITOR’S NOTE: I’m not a medical professional and I’m not a statistician. There’s a lot we don’t know about COVID transmission on airplanes. And so on. But the point remains the same, and valid: Think about what you’re going to do before you do it. Full disclosure: I’m personally considering a trip to Florida to visit my elderly mother.

If what you just read pisses you off, that’s because it’s something nobody else is telling you, and that’s valuable. How valuable is up to you: We offer two options: You can send cash to PayPal in order to help support us, or you can buy us a coffee. We can use the morale boost — and the caffeine, particularly now that post-COVID fatigue has set in.

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