So when it comes to COVID-19, how safe is air travel?
This is a common question
I get asked all the time.
And it's really interesting
because we have some data on this, not nearly enough
but enough to really have a good conversation.
So let's do that now.
Recently,
there was a study
of a long haul flight, about 18 hours
Uggggh
It gives me the hives just thinking about it
from Dubai to New Zealand.
Now the locations are important
because New Zealand has a very aggressive quarantine policy
for people who land in the country.
So it's like a 14 day mandatory quarantine.
So during that time
people are surveillance tested for coronavirus
and so it's a pretty controlled environment
probably a really good environment
to do a study on airplane transmission.
So during this flight from Dubai to New Zealand
it turns out there was an index case
a person who was infected,
or it might even be two people out of seven
who were infected when they boarded the flight.
And we know this by looking at the epidemiologic data
that happened afterwards
after people started testing positive,
ultimately a total of seven people tested positive
while they were in quarantine in New Zealand.
And what they found was the genetic lineage
of that virus was the same in those seven people.
So most likely they were sharing the same virus.
Now you can only find that out
if you do genomic testing on the actual virus
you don't just do
the Cepheid GeneXpert PCR test
you have to follow up
with actual genomic sequencing of the full RNA.
And they did that in this case
because the New Zealanders are crazy about that stuff.
So in that case, they were able to say,
okay, they all came, the virus all is the same.
So in this cluster of seven people
where was the transmission occurring?
So they went back and realized, okay
they were sort of required to get screened
before getting on the plane with testing.
It turns out the guy who was a guy or girl
who was positive before getting on the flight
there was an error,
it was presumed that he tested negative 48 hours
before getting on the flight
but it was actually four days prior.
Now this is interesting
because that means that that negative test,
whether it was a false negative
or something else where he got infected
after that was not enough screening
to prevent him from boarding that plane
with an asymptomatic at that time case of coronavirus.
The others got tested as well
they were negative getting on and got on the flight.
Now all of the people were sitting in aisle seats
within the same four rows on this 18 hour flight.
So they were relatively close to each other
but they weren't necessarily all in the same row,
but within four rows.
Now, why is this important?
Well, it turns out if you're gonna be on an airplane
it is one of the safest place...
A modern aircraft is one of the safest to be
from an infection standpoint
or ventilation standpoint of any confined space.
And the reason is modern aircraft use HEPA filters
to circulate their air.
HEPA filters capture very tiny particles from air
and the way that this filtration works is that
you have air flow coming from the ceiling
and it goes underneath basically the window seat
under the window.
That's the path of airflow.
And this path of airflow is a laminar
that's a physics term, which means it's not turbulent
it's not like circulating everywhere
and causing clouds like
in those Charlie Brown cartoons
where you see Pig-Pen
and he's got a cloud of dust around him and flies and stuff.
It's this very smooth flow
non turbulent flow that carries particles
out and through the HEPA filters.
Now the entire air volume of the airplane
is actually changed every three minutes
while you're cruising, while you're in the air
and all this equipment is running.
That's important.
That's an important distinction.
And on top of that, about 40% of the air is recirculated
in the plane through these HEPA filters
and the other 60% is fresh air
piped in from outside the craft.
So it's a pretty aggressive ventilation inside planes.
Now we know that ventilation is part of the component of it
the other component of it is,
well ventilation is not gonna help you
HEPA filters aren't gonna help you
if you're right next to somebody
and they spew droplets that contain the virus
because that virus is gonna end up in that flow
getting to you, going in your mucus membranes
going in your eyes
and infecting you or landing on a seat, armrest
you touching the armrest you're rubbing your face
that's a lesser mode of transmission but it can happen.
So back to this flight,
these guys were four rows apart
of the people who got infected
two of them did not report wearing masks.
Now this is the thing: masks are often required by policy,
they're not a law in the U S by the way
but they're required by policy on most airlines
but the degree of enforcement varies.
And on top of that, remember
that you can take your mask off and have to
in order to drink and eat and on an 18 hour flight
there's gonna be a lot of that going on.
So there probably wasn't fully consistent mask wearing
I think people were wearing gloves too
for some of these passengers that were infected
but a couple of them didn't even report wearing mask,
but the others did and still got infected.
But what's interesting too,
is that others in those rows did not get infected.
And one of the people infected was presumably infected
after the fact in quarantine
because when they made the diagnoses
people started testing positive later during quarantine
and the index case who was asymptomatic
and this is often the case actually developed symptoms.
So they weren't REALLY asymptomatic,
they were pre symptomatic.
And therefore probably had a higher viral load
because remember if you're purely asymptomatic
if you never develop symptoms, but you test positive
it's likely that your viral load
and your infectivity was not all that high
but if you were presymptomatic
in other words you just hadn't shown symptoms yet
but you're gonna show symptoms
at that time your viral load could be very high,
it could be replicating all over the place
and that may have been what happened with this guy.
So what's interesting about this case
is in Kuala Lumpur they did a stopover
18 hour flight's a long time,
you have to stop refuel, during that two hour stopover
the power equipment on the plane
actually was shut down for some reason
whether it was a mechanical issue
or something else for about 30 minutes
and they were on the ground for two hours.
Remember all that air exchange
on the flight happens when the equipment is up and running.
So for 30 minutes,
there was no good ventilation on that plane
and everybody's breathing their own stink air.
And if you've ever been on a flight
and you're sitting on the tarmac and you smell jet fuel
and you smell farts, that's what's happening is
the ventilation is not really happening.
We've all been in those situations, right?
Your neighbor, you're just like, damn
homie couldn't you just like hold it in a little longer?
So in that setting there was a possible,
it could have been that transmission happened at that point
we don't quite know
but the picture that you're starting to experience here
is what they call the Swiss Cheese Model of system failure.
So where did the transmission occur?
Well, if everything were going right
there are multiple layers of cheese that are protecting you
each one has a hole or two in it where it could fail.
And so if Swiss cheese one
there's a hole and you get through it,
Swiss cheese two is lined up a little differently
maybe it blocks you right
and Swiss cheese three.
But there are rare times where all the Swiss cheese
and all the holes line up and you go right through.
And in this case it could have been poor ventilation,
it could've been the missing link
of the person not getting tested.
So if he had been tested two days prior
to the flight that he or she, that might've caught it
and wouldn't have gotten on the plane
would have prevented the transmission.
If the ventilation system hadn't failed on the ground
it might've prevented transmission.
If the people who weren't wearing masks wore masks
that might've, if they were all wearing higher grade mask
high fidelity masks, like KF94s
or N95s
which as we see increasingly contagious variants emerge
those might be more efficient masks.
We know they work
in medical settings in high-risk procedures
and they have very, very good protection, right?
As we start to get more vaccination
and more people vaccinated
we'll have a threshold for infection
or a higher threshold for infection
and there'll be less spread on airplanes.
So going back to this case
people started testing positive
then after the fact,
one of them caught it in quarantine
which again speaks to the local
sort of household transmission that's very common.
And then, so back to the prime question
is it safe to fly?
The answer is well, maybe, and maybe not
and it depends on how many
of those safety mechanisms are in place,
how careful the passengers are,
how well the equipment's working,
how good the screening is, right?
So if we're talking about recommendations
as this virus potentially
becomes variant in a way
that makes it a little more contagious
as we spin up vaccinations but they're slow,
it might make sense
that people are more compliant with masking on flights
when you're in enclosed areas,
maybe the mask quality should be higher,
maybe you ought to be double bagging your mask
or using a KF94 and N95
we'll probably do a show on that at some point.
Getting as many people vaccinated as you can,
doing the testing
'cause that's gonna be important
and then studying the living crap out of it,
New Zealand did it but guess what?
How many flights in the United States
do you think there were
that where transmission occurred
where we have no effing clue when and how it happened?
Probably the vast majority of any spread
that's occurred on airplanes
has occurred in a way that we haven't been able to track it
because we don't do the contact tracing,
we don't do the testing,
we don't do the study,
we don't follow up,
we don't do the genomic testing
to see are these viruses the same.
And so it's just total chaos here.
But we can look at people who've done it correctly
and then learn from it because believe me, man,
this is still just a warmup
for a pandemic that has a high even higher fatality rate
and a higher contagiousness
and at some point that's coming.
So the other thing that may be useful
is rapid antigen testing at the point of boarding the plane
because those tests often are positive
only when people are highly contagious
and have high viral loads
you can still have false positives
but that might be a way of
that final sort of Swiss cheese lining up and saying,
Okay don't get on the plane
because you're actually contagious
and don't even know it, right?
And you can follow up with real testing.
So there are ways to fly safely.
There are ways to open up again.
There are ways to science the crap out of this
and we have to do it.
I'm gonna put some links in the show notes
to articles you can read
with further links to learn more about this stuff.
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All right, guys, I love you.
We are out, peace.