It's almost Back to School time & we're still seeing about 100k cases a day here in the US.
How do we stop COVID from going back to school too?
Our new pre-print confirms face masks must be part of our plan!
Let me explain /🧵
medrxiv.org/cgi/content/sh…
How do we stop COVID from going back to school too?
Our new pre-print confirms face masks must be part of our plan!
Let me explain /🧵
medrxiv.org/cgi/content/sh…
"What did we study?"
Halfway through the 2021/22 school year, some Massachusetts school districts dropped their mask requirements. This created a natural experiment.
We estimated: The causal effect of removing mask mandates in those districts on COVID levels
Halfway through the 2021/22 school year, some Massachusetts school districts dropped their mask requirements. This created a natural experiment.
We estimated: The causal effect of removing mask mandates in those districts on COVID levels
"What did we find?"
School districts which removed mask policies had an immediate increase in COVID cases in both students and staff.
This increase in cases got bigger over the next 10 weeks.
School districts which removed mask policies had an immediate increase in COVID cases in both students and staff.
This increase in cases got bigger over the next 10 weeks.
"How much did removing mask policies matter?"
Schools which removed mask policies had an average *increase* of 44.9 cases per 1,000 people over a 15 week period compared to if they had not removed their mask polices.
This adds up to an estimated 11,901 *extra* COVID cases!
Schools which removed mask policies had an average *increase* of 44.9 cases per 1,000 people over a 15 week period compared to if they had not removed their mask polices.
This adds up to an estimated 11,901 *extra* COVID cases!
Implication: No mask requirement means kids miss school!
We estimated that students had an average increase of 39.9 cases per 1,000.
If all students who tested positive followed state guidelines to isolate for 5+ days, that's almost 20,000 *extra* missed school days!
We estimated that students had an average increase of 39.9 cases per 1,000.
If all students who tested positive followed state guidelines to isolate for 5+ days, that's almost 20,000 *extra* missed school days!
Implication: No mask requirement means teachers & school staff miss work!
For all staff, we an estimated 81.7 extra cases per 1,000!!
That's how many *more* teachers & staff got sick with COVID than would have if those school districts had kept mask requirements in place.
For all staff, we an estimated 81.7 extra cases per 1,000!!
That's how many *more* teachers & staff got sick with COVID than would have if those school districts had kept mask requirements in place.
"What about alternate explanations?"
School districts that dropped mask requirements tended to have better budgets, better buildings, better vaccination rates, and lower community COVID levels.
Our study shows those weren't enough to make dropping mask mandates work!
School districts that dropped mask requirements tended to have better budgets, better buildings, better vaccination rates, and lower community COVID levels.
Our study shows those weren't enough to make dropping mask mandates work!
"Why should you believe our study?"
This study is not a randomized controlled trial, it's an observational study, but it *can* still tell us about cause and effect.
For details on why & how the approach we used works, see this earlier thread:
This study is not a randomized controlled trial, it's an observational study, but it *can* still tell us about cause and effect.
For details on why & how the approach we used works, see this earlier thread:
https://twitter.com/EpiEllie/status/1555322752810291201?s=20&t=O-aitRhzXHsfCmgU9RTv7w
Bottom line:
Eastern Massachusetts school districts which removed mask requirements in March 2022 saw a *dramatic increase* in COVID cases compared to if those districts had retained mask requirements.
And this was *despite* all other mitigation efforts those districts did.
Eastern Massachusetts school districts which removed mask requirements in March 2022 saw a *dramatic increase* in COVID cases compared to if those districts had retained mask requirements.
And this was *despite* all other mitigation efforts those districts did.
A huge thank you to the team at @HealthyBoston who worked so hard on this study, including lead author Dr Tori Cowger & senior author @KTHallPhDMPH, plus the rest of the amazing team: @OjikutuBisola, Sarimer Sanchez, Jaylen Clarke, @DrNataliaLinos, & @DrMaryTBassett.
Here's a link to the pre-print for those that want to delve more deeply into the science: medrxiv.org/content/10.110…
Adding to say: First author Dr Tori Cowger’s twitter is @ToriCowger (which I probably should have guessed😆🤦🏼♀️)
One last thank you: to #econtwitter who do an excellent job of summarizing & tracking advancements in methods, and helped me stay up to date on new & improved DiD estimators over the past year.
A few people are critiquing this study saying that getting rid of mask policies simply means more kids were tested for COVID. I disagree, because we didnt just look at contact tracing.
But even if were a little true this critique actually strengthens the evidence for mandates!
But even if were a little true this critique actually strengthens the evidence for mandates!
https://twitter.com/fakecarlhill/status/1557425734540476417
Why?
If, as these critics themselves are claiming, lifting mask mandates means more kids are tested and so more kids test positive, that STILL means lifting mandates causes more missed days of school — even if it only changes detection not transmission!
If, as these critics themselves are claiming, lifting mask mandates means more kids are tested and so more kids test positive, that STILL means lifting mandates causes more missed days of school — even if it only changes detection not transmission!
So, no matter whether you believe our interpretation of the data that there are more *total* cases without mask mandates, or you believe the counter-interpretation that there are more *detected* cases, you still have to end up at mask mandates keep kids in school!
The point here being that, no I don’t think there’s any reason to suspect detection is what changed, and also that any critique which relies on everything about our study being correct except the final conclusion, is a pretty weak criticism 🤷🏼♀️
Some people are asking why we didn’t control for “obvious” confounders.
The simple answer is: we did. The method we used implicitly controls for all of the differences between districts that don’t change over time.
The simple answer is: we did. The method we used implicitly controls for all of the differences between districts that don’t change over time.
Why should you believe me?
My research expertise is specifically in how to control for confounding (and other biases) in health research so we can get good answers to clear questions.
I did my doctorate on this at Harvard and I work on it every day at Boston University.
My research expertise is specifically in how to control for confounding (and other biases) in health research so we can get good answers to clear questions.
I did my doctorate on this at Harvard and I work on it every day at Boston University.
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