There’s a remarkable piece out in the New York Times today that calls out the CDC for “DRAMATICALLY overstating the risk of outdoor transmission” of COVID-19:
The CDC has been DRAMATICALLY overstating the risk of outdoor transmission.
They claimed it's been "less than 10 percent." It's a lot closer to .1 percent.https://t.co/UldJgUXYk0 pic.twitter.com/qI6jd0nCf4
— Vince Coglianese (@VinceCoglianese) May 11, 2021
Holy s*it is this bad:
"A Misleading CDC Number… Saying that less than 10 percent of Covid transmission occurs outdoors is akin to saying that sharks attack fewer than 20,000 swimmers a year. (The actual worldwide number is around 150.) It’s both true and deceiving."https://t.co/NhUnLF5Zdr
— Jerry Dunleavy (@JerryDunleavy) May 11, 2021
NYT journo David Leonhardt breaks it down in this long thread that’s well worth a read:
The CDC says that “less than 10%” of Covid transmission occurs outdoors.
Which sounds like a lot of outdoors transmission. If anything close to 10% was correct, it would mean thousands of deaths were from outdoors transmission.
But the number doesn’t stand up to scrutiny. 🧵
— David Leonhardt (@DLeonhardt) May 11, 2021
If you read the academic research that the CDC has cited in defense of the 10% benchmark, you will notice something strange. A very large share of supposed cases of outdoor transmission have occurred in a single setting: construction sites in Singapore.
How could that be?
— David Leonhardt (@DLeonhardt) May 11, 2021
It turns out that academic researchers defined places that were a mix of indoors and outdoors as outdoors.
One study defined all of these settings as outdoors: “workplace, health care, education, social events, travel, catering, leisure and shopping.”
— David Leonhardt (@DLeonhardt) May 11, 2021
In the case of Singapore, some of the supposedly outdoor construction sites had many enclosed spaces.
So there is a very good chance that many of these transmissions classified as outdoors were actually indoors.
— David Leonhardt (@DLeonhardt) May 11, 2021
And yet even counting all the Singapore cases as outdoors still suggests only about 1% of transmission was outdoors.
Other studies — from Ireland and China — put the share at 0.1% or less.
— David Leonhardt (@DLeonhardt) May 11, 2021
Note: The Singapore study on construction sites is even more flawed than reported in the NYT:
Also on the Singapore construction sites. (I also chased down the same number for my recent NYT piece). Besides the shared dormitories, they do work at loud environment all day: yelling at very close distance. That's probably how you can get those rare outdoor transmission cases.
— zeynep tufekci (@zeynep) May 11, 2021
At very close distance, (0.2 to 0.5 meter) you *are* spraying people a bit more with larger particles, and the smaller aerosols are more concentrated there, too (will dilute quickly outdoors but at first that' where they are.) See correct graphic: pic.twitter.com/z13WXEH33m
— zeynep tufekci (@zeynep) May 11, 2021
So construction or similar people singing/yelling at very close distance may allow transmission even outdoors, especially if prolonged. (Which fits what we know from the epidemiology). So that's the outdoor rule for me: avoid close, prolonged contact between the unvaccinated.
— zeynep tufekci (@zeynep) May 11, 2021
But also that agree with Muge Cevik that the Singapore sites also had shared dormitories (which is what my own chasing down of that number revealed) so that was likely indoors/outdoors in many cases. Thanks for getting the more correct number out.
— zeynep tufekci (@zeynep) May 11, 2021
Back to the thread:
Saying that less than 10 percent of Covid transmission occurs outdoors is akin to saying that sharks attack fewer than 20,000 swimmers a year. (The actual worldwide number is around 150.) It’s both true and deceiving.
— David Leonhardt (@DLeonhardt) May 11, 2021
The CDC’s exaggeration of outdoor transmission isn’t just a gotcha math issue. It is an example of how the agency is struggling to communicate effectively, and leaving many people confused about what’s truly risky. https://t.co/4LiYI2WdUx
— David Leonhardt (@DLeonhardt) May 11, 2021
The government list of recommendations is so long and complex that it’s useless to many people, as @zeynep has noted.
All the while, the scientific evidence points to a much simpler conclusion: Masks make a huge difference indoors and rarely matter outdoors.
— David Leonhardt (@DLeonhardt) May 11, 2021
Britain, notably, seems to have figured this out. Officials have been more aggressive about restricting indoor behavior — and aren’t trying to get people to wear masks outdoors.
Despite the outdoor masklessness, Covid deaths are down 99+%. https://t.co/4LiYI2WdUx
— David Leonhardt (@DLeonhardt) May 11, 2021
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