Joseph Allen Profile picture
Assoc Prof @HarvardChanSPH; Lancet @CommissionCOVID (Chair Task Force on Safe Work/School/Travel); Coauthor of HEALTHY BUILDINGS @Harvard_Press; WaPo, NYT, HBR
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Apr 21 23 tweets 6 min read
One of the real challenges in interpreting risk on airplanes is the massive denominator. When a plane crashes, it's rightly front page news, but doesn't mean flying isn't safe. Same issue w/ unruly passenger, jerky comment about masks, some guy playing guitar in the aisle...

These issues make 'front page news' on social media, but they're wholly unrepresentative. (I flew two days ago, and about 10-20% chose to wear masks, no flight attendants did, and nobody seemed to care either way. It was blissfully boring, and gets lost in the denominator.)
Apr 5 4 tweets 1 min read
Sorry, but this one is very straightforward

Ventilation and filtration work
-planes exceed the highest ‘clean air delivery rates’ anywhere, including surgical suites

1/n… N95s work
-If not comfortable w masks off, you can wear an N95. This is excellent protection, no matter what your seatmate is/is not doing.

Apr 2 7 tweets 2 min read
Well, this caught my eye. I led point on LD outbreak investigations and thought I’d seen it all, but never saw this. And, after reading it, I’m not buying the conclusion.

1/n First glance issue is the exposure pathway. I’m having a hard time with it - aerosolized washer fluid on windshield that penetrates the truck cab? I guess maybe…

Mar 27 16 tweets 3 min read
"an important flaw exists in how most buildings operate in that the current standards for ventilation and filtration for indoor spaces, except for hospitals, are set for bare minimums and not designed for infection control"

THE SOLUTION: 🧵👇 "Increasing air changes per hour and air filtration is a simplified but important concept that could be deployed to help reduce risk from within-room, far-field airborne transmission of SARS-CoV-2 and other respiratory infectious diseases."
Feb 25 20 tweets 4 min read
"just about every building you’ve ever walked into is underventilated with low levels of filtration. That’s b/c the standard that governs ventilation rates is a bare minimum not designed for health."

We need Operation Warp Speed for clean *indoor* air
🧵… When we think about the full suite of tools we need to combat covid, now and in the future, we’ve had many successes - vaccines, therapeutics, rapid tests. But amid all these achievements, one of the most important and needed has been ignored: good ventilation and filtration.
Feb 24 4 tweets 2 min read
Great to see this profile of terrific colleague and friend @CellDeathLab and his team.

—> “lungs of the elderly offer up many more targets for the virus to latch onto compared with young lungs, which could help explain the sharp disparities in disease severity by age.” I’ve been flagging this paper since it was a preprint. Can’t stop thinking about it. Some people had ‘almost no’ ACE2 gene expression?!?
Feb 6 4 tweets 2 min read
What do crypto, gamestop, and NFTs have in common? Read these 3 articles, then you’ll know (hint: the short answer is in the penultimate sentence in one of them)

@jodyrosen @mccabe_caitlin @amandamull

🧵 Crypto👇
Feb 4 8 tweets 3 min read
The importance of wastewater for routine surveillance is gaining traction. Two new tools just got released yesterday 🧵

1. National Wastewater Surveillance System dashboard

(It’s a start. Best part is there are plans to expand this across the country)
Jan 14 13 tweets 3 min read
Relying on the 2020 playbook as we head into 2022 is as foolish as relying on the 2019 playbook as we entered 2020. The game has changed. Given the availability of vaccines, here are 10 updates to the playbook for 2022 (from 12/15. Still holds.)

🧵… 1: “Fully vaccinated” should mean you’ve received a booster shot.

Your body needs to “see” the signature of this virus again to restore protection against the delta and omicron variants.
Jan 11 10 tweets 3 min read
8 degrees in Boston. No outdoor activities at school.

My 9 year old: "So no mask breaks today? That's worse than freezing."

Don't tell me 2 years of masking doesn't impact kids. Their risk is low, vaccines avail for all adults and kids, anyone who wants can mask. It's time.
Jan 3 14 tweets 3 min read
Make no mistake, the costs of closing schools is high. Too many have gotten casual about this.

A thread.… "Even short-term closings have steep consequences. Schools are the place where we first detect trouble at home, including neglect and abuse."
Dec 29, 2021 17 tweets 6 min read
I see a lot of people - on both "sides" - making simple mistakes about masks. I've studied PPE, taught PPE, and overseen PPE programs, including teams implementing fit testing in hospitals, long before covid.

A thread 1. Masks work

It's basic physics.…
Dec 20, 2021 4 tweets 2 min read
1. Vax/boost are key (I said about 40x...)
2. Not reckless for NFL to stop routine testing of vaxxed. Were doing 1x a week which is a surveillance strategy, not a control strategy. (you've seen viral kinetics of Omicron, right?)

continued... 3. Overestimating transmission risk on the field (they have good ventilation/filtration in locker room, trainer, weight room...right? RIGHT??)
4. Overestimating superspreader risk in large volume spaces, like outdoor stadiums (and even indoor arenas)

Dec 4, 2021 6 tweets 3 min read
It was never a question of if, only a question of when. And when that when happened, we knew buildings would play a key role in the a response.


1. ANTICIPATE (Dec 2, *2019*) 2. RECOGNIZE (Feb 9, *2020*)

"Even with this uncertainty, it is clear that we can enlist buildings to help us in this fight."…
Nov 29, 2021 5 tweets 1 min read
This picture is creating misplaced outrage bc Biden is in a surgical mask instead of an N95.

1. Yes, N95s or KF94s are better if you need to wear a mask


2. Everyone is fully vaxxed and boosted, so masks provide limited benefit (especially considering 5 and 6)
🧵 3. Even though surgical mask has lower efficiency, the combined efficiency of two 70% masks is 91%. Saying they’re useless is incorrect.
Nov 27, 2021 4 tweets 2 min read
What can schools do right now, if feeling anxious and don't want to wait 2 weeks til Omicron gets sorted out? Implement the simple tips from our Lancet COVID19 Commission report:…

(BONUS...improvements to school buildings come with many other benefits!) ImageImage Where’d the ‘2 weeks’ come from? 👇
Nov 20, 2021 4 tweets 2 min read
Some people have have high ACE2 expression, and some have “almost none”

For the life of me, I can’t figure out why so few have engaged with this research that’s been out as preprint from @celldeathlab for over a year…

Nov 4, 2021 5 tweets 3 min read
Jan 2020: rapid tests (@RanuDhillon; @sri_srikrishna)
Feb 2020: ventilation; filtration; portable air cleaners (me)
Mar 2020: airborne (@linseymarr)
Mar 2020: masks (@zeynep)

We knew what it was, how it spread, how to test, and how to stay safe before vaccines *very* early on
🧵 Jan 2020: rapid tests (@RanuDhillon; @sri_srikrishna)…
Oct 22, 2021 6 tweets 2 min read
Here are 4 things we should do to prioritize the health of children:

1⃣ Mandate vaccines for all adults in schools
2⃣ Host at-school vax clinics in every school
3⃣ Expand use of rapid antigen tests
4⃣ Improve ventilation and filtration

Details in thread… 1⃣ "Mandate vaccines for all adults in schools, as Los Angeles and New York City have done. We know this causes vaccinate rates to rise sharply. New York City’s Department of Education saw its rate spike from around 50 percent in early August to 95 percent."
Oct 22, 2021 8 tweets 2 min read
Many masking policies rely on these two CDC metrics. They’re deeply flawed. How has this escaped scrutiny?

“CDC primarily uses two metrics: seven-day-average case numbers per 100k people and the rate of tests that come back positive. Both have problems.”… “The first metric might seem reasonable, until one recognizes that there are vast differences in risk by vaccination status and by age. Vaccinated people are 29 times less likely to be hospitalized than the unvaccinated, and children are hospitalized at low rates, too.” 2/
Oct 16, 2021 4 tweets 1 min read
This backlash was predicted. We shouldn’t extend controls beyond what’s necessary, or else we lose trust. The pushback is not coming from hoaxers or anti-maskers or anti-vaxxers - and it’s not limited to this campus. The window is closing on rational people accepting this…
🧵 👇