1/ Stay in your seat and remain calm.

This report is making the rounds.

I read it. (including appendix, which I'm guessing few read, b/c if you did....)

https://wwwnc.cdc.gov/eid/article/26/11/20-3299_article

2/ For background, flight was from early March, 10-hour flight, thorough attempt to contact all passengers. A massive lift, so nice work by the authors on that front.

3/ Index patient had active symptoms, actively coughing, no masks

First takeaways:

-airplanes are vectors of disease, moving people around countries and globe and spreading
-this person was irresponsible

*stay home when sick*

4/ big picture numbers:

This is 1 flight from March (and I'm not totally convinced in-flight transmission happened, as you'll see in a sec)

For context, TSA logged 4.7M passengers in just past 7 days

If planes were hot beds of spread, we'd see more...a lot more

5/ I made this point in op-ed from May:

"Billions of people travel by plane every year, yet there have only been a handful of documented disease outbreaks attributable to airplanes in the past 40 years." https://www.washingtonpost.com/opinions/2020/05/18/airplanes-dont-make-you-sick-really/

6/ Can you get this on an airplane? Yes, sure, you can get this virus anywhere. Time on airplane is just lower risk than people think.

People tend to point to the airplane first, ignoring the other travel-associated activity

Now, to the report...

7/ They report 15 "flight-associated" cases, and rule out that these travelers had pre- or post-flight exposure.

First thing that caught my eye showing that this couldn't be correct:

"median symptom onset was 8.8 days (interquartile range 5.8–13.5) after arrival"

hmmm...

8/ CDC reports median incubation period of 4-5 days, with 97.5% of symptoms showing within 11.5 days.

A sign we should dig deeper in this airplane study...

9/ And when you dig, you uncover. Things like this:

"We also note that cases 3 and 14 experienced symptom onset 17 days after flight VN54."

17 days after the flight!

Yet, the authors say these are 'flight-associated'.

(there's more...)

10/ five of the 15 "airplane-associated' cases had symptoms beyond the time when 97.5% of people have symptoms (11.5 days)

Unlikely these five people caught this on flight.

11/ So, the '15 cases of airplane-associated cases' is already down to 10 with just some basic review of symptom data.

What else can we learn about those other 10...

12/ The authors took pains to explain away post-flight transmission:

"We consider local transmission after arrival in Vietnam unlikely."

But when you peek at the appendix, you find more info that suggests post-flight exposure occurred...

11/ in addition to the symptom data supporting that post-flight exposure happened, so does the time-activity info

There sure seems like *a lot* of important post-flight exposure activity

Like this: 3 of the 'flight-associated' cases went on *CRUISE SHIPS* after flight (blue)

12/ Really, look at that figure hard

Combine it with the earlier statement that median incubation was 8.8 days after flight, as opposed to 4-5 days from CDC

Walk back 4-5 days from when their symptoms appeared.

--> cruise ships and hotels is what you see

13/ For example:

Case 2
Symptom onset March 10

activity 5 days before? cruise ship

(same with Case 3)

14/ It is certainly possible some got this on the airplane - the index patient person was actively shedding and coughing + no masks.

And strongest evidence here that there might have been transmission on airplane is several cases adjacent to business class.

15/ if you take out those people who had symptoms well beyond incubation period (meaning, they were unlikely to have gotten this from the flight), does Figure 1 that shows the dense clustering (the strongest argument the authors make), look different?

15/ eg, Case #4, 10, and 11 are only ones w/ symptoms within 6 days of flight.

Does Figure 1 look different if it only shows these 3 cases as 'airplane-associated' cases?

15/ One way to explore this more is look more closely at the time-activity data and symptom onset in relation to seat location on airplane, but I don't see a way to link the data from the seating chart (fig 1) to time-activity data in appendix)

16/ genomic sequencing would answer this...

17/ Taking a step back

You can get this virus anywhere.

There been millions of travelers since this flight yet one report (similar to SARS).

Could be more, sure, but overall rare.

And this report is not as airtight as the headline and abstract (and news reports) make it seem

18/ Big picture: I stand by statement I made in op-ed in May.

-time on airplane is lower risk than other parts of travel
-masking on airplanes right now is a must
-take precautions
-only travel if really necessary
-STAY HOME WHEN SICK https://www.washingtonpost.com/opinions/2020/05/18/airplanes-dont-make-you-sick-really/