Matt Malkus Profile picture
15 Oct, 17 tweets, 6 min read
1/ I earnestly looked into this, because I wanted to know how they arrived at these results.

"[B]ased on predictive models, COVID-19 impacts could be lessened by up to 47% if a majority of people wear masks."

Oh, boy, predictive models? I thought we'd learned our lesson here.
2/ "Predictive model" here is a fancy way of saying "our results are based on parameterized inputs, not empirically observed data."

Still, let's give them the benefit of the doubt, shall we? Here's the paper. Let's dive in! ijidonline.com/article/S1201-…
3/ As expected, the model is based on parameters derived from other literature.
On masks:
"We chose a conservative non-medical mask efficacy, eM = 20%, within the estimated range for reducing disease transmission during interactions between susceptible and infected individuals."
4/ They refer to 4 papers as justification for their parameter. Let's look at the first one (Davies et al. 2013).

"[T]he homemade mask did not significantly reduce the number of particles emitted (P = .106)."

Oh?

ncbi.nlm.nih.gov/pmc/articles/P…
5/ This paper concludes:
"[T]hese masks would provide the wearers little protection from microorganisms from others persons who are infected with respiratory diseases. ..[W]e would not recommend the use of homemade face masks as a method of reducing transmission of infection"
6/ Well, maybe let's try the next one (MacIntyre et al, 2015).

Some of you may recognize this paper! It's been frequently cited... by those panning the efficacy of cloth masks.

It famously found *higher* infection rates from cloth masks than the control.
bmjopen.bmj.com/content/5/4/e0…
7/ As a refresher: "This study is the first RCT of cloth masks, and the results caution against the use of cloth masks. ... Moisture retention, reuse of cloth masks and poor filtration may result in increased risk of infection."

OK, so this "new" mask efficacy model is 0-for-2.
8/ The other two papers are from 2020, so I don't have high hopes in their rigor, but let's continue to indulge.

Here is Konda, et al (2020). It essentially places different materials on the end of a tube and circulates air around to see what percentage of particles get through
9/ You may be thinking: "Hmm, doesn't seem to realistically represent mask-wearing in public."

The authors acknowledge this!

"[I]n the realistic situation of masks worn on the face without elastomeric gasket fittings (such as the commonly available cloth and surgical masks)...
10/ So, in conclusion, Konda finds that masks fitted as tightly/properly as N95s can reduce aerosol transmission substantially, but that in the "realistic situation" that your commonly available mask doesn't fit that way, it's probably 60% less effective.

pubs.acs.org/doi/pdf/10.102…
11/ One more paper! Here is Mondal et al. (2020). This is one commonly cited by proponents of mask-wearing. It is a meta-analysis, of sorts (only 10 papers) - two of which we've already covered (MacIntyre, Konda).
medrxiv.org/content/10.110…
12/ The limitations identified by the authors are pretty broad. Namely:
"Only one randomized controlled trial evaluated cloth
masks for their efficacy in preventing infection by respiratory pathogens"
Yep, that was MacIntyre - the paper that found *higher* infection with cloth.
13/ 7(!) of the 10 papers covered by this study focused on filtration efficacy of material. Only two used "healthy volunteers," i.e. humans. One was Davies, 2013 (see tweets 4 and 5 - they don't recommend cloth masks!). The other was van der Sande, et al. (2008). They found:
14/ OK, so some minor benefit of masks.

I decided to look up the van der Sande paper, though, for the hell of it.

Take a look at what else is in the conclusions: "Given the need for the population to acquire sufficient natural immunity over time..."

Oh no! Not herd immunity!
15/ So, in conclusion: The new paper by Zhang et al. which claims mask-wearing would reduce infections/deaths by 47% assumes that masks are 20% effective. They cite 4 papers to support this assumption. 2say they don't work at all. 1 is mechanical. 1 advocates herd immunity.
16/ The paper also advocates for shelter-in-place efforts (funny since they indirectly source their mask efficacy parameter from a paper that advocates herd immunity), and don't explain why 1 mask-wearer = 20% effective, but 2 = 36% effective.

This is apparently science.
Addendum: I really don't care a lot about masks. Think they aren't very intrusive, possibly small benefit, esp. in prolonged encl. contact.

Studies (& esp. news coverage) like this makes them out to be far more effective though. May actually be harmful (may reduce distancing!)

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More from @malkusm

14 Oct
Thanks, Meghan, for covering tonight's board meeting. I appreciated the opportunity to meet with concerned parents and teachers beforehand, and to lay out some of the facts surrounding the costs of school closures for the board.

References to statements I made follow (THREAD).
Count/list of Texas school districts who have announced an end to in-person learning, and selected statements from school districts which did so. Thanks @therealarod1984 for compiling and staying on top of this.
I made two references to independent studies of absenteeism in schools and the widening gap between students in affluent districts versus those in poor/impoverished districts. Here is the first, from the Dallas Morning News, covering 80 districts. dallasnews.com/news/education…
Read 8 tweets
9 Sep
Hey, what ever happened to the "COVID kids develop Kawasaki disease" storyline that was used to terrify parents back in April or May?

Well, the CDC didn't forget - they published a report on August 4 on the... wait for it... *565* total cases in the US.

cdc.gov/mmwr/volumes/6…
Through September 3, there have been about 515K cases of COVID-19 in children.

There are roughly 55 million school-aged children in the US.

services.aap.org/en/pages/2019-…
So, to recap:

- Less than 1% of all school-aged children in the US have tested positive for COVID;

- Of those, about 0.1% developed Kawasaki-like disease (MIS-C);

- Of THOSE, only 1.8% (10 total persons) died.

So, I wonder why you never heard these numbers?
Read 5 tweets
22 Aug
Something that people have a hard time grasping:

Taking COVID-19 seriously and demanding transparent, accountable, science-based government are not mutually exclusive.

I'd demand answers to questions about our policy response even if the death toll were 100x what it is today.
Good public policy should:
- Properly assess the risk and the benefit of action
- Properly assess the cost of each action & weigh it against the benefit
- Be clearly communicated to the public, including specific goals
(ctd.)
- Be non-arbitrary (i.e. grounded in logic, facts, relevant data)
- Account for ALL stakeholders, i.e. all members of society (rich, poor, young, old, etc)
- Be re-evaluated regularly as part of a discussion involving the public (not by decree)
Read 4 tweets
5 Aug
Meet Steven Manzo, a tragic casualty of lockdown. A recovering addict who overcame so much, and had so much life ahead of him.

#RIPStevenManzo

Next time you advocate for the closure of a business, school, or other aspect of society, remember Manzo.

Then multiply his case by...
5,000: Roughly the increase in national overdose fatalities from March to May, based on these % increases above the CDC's 2018 baseline. washingtonpost.com/health/2020/07…
10,000: The estimated increase in breast & colorectal cancer deaths over the next 10 years due to missed cancer screenings. "This analysis is conservative," says the author, director of the U.S. National Cancer Institute. science.sciencemag.org/content/368/64…
Read 14 tweets
29 Jul
Let's take a trip down #SARSCoV2 memory lane, shall we?

Here's one of the big misses from early estimates which informed @IHME_UW modeling, and ultimately policymakers: "15-20% of those who contract [COVID] will need hospitalization," said Dr. Fauci.
As some started to realize that there would be no avoiding the virus here in the US, hospital capacity was the singular focus. It was never about suppression.

After all, we only have so many hospital beds, PPE, etc - we needed to "flatten the curve."
By March 6, we're approaching the critical days when the world began to change. We had compelling visuals on what it meant to "flatten the curve":
- Buy time
- Reduce peak health care utilization
- Prolong the epidemic at manageable levels
Read 17 tweets
28 Jul
COVID+ athletes have been big in the news recently. The Miami Marlins had an outbreak in the last 24 hours. It's the latest in a laundry list of news stories about athletes testing positive.

Should we be concerned?

You be the judge - here is the breakdown of symptom severity.
No doubt, in rare cases, COVID can cause health complications & lingering issues. This is the case of Red Sox pitcher Eduardo Rodriguez, who is experiencing lingering cardio issues. He's in the <2% of "Severe Illness" group (and <1% with lingering effects)
Far more common, though, are cases such as Russell Westbrook: Athletes who test positive are completely asymptomatic nearly 60% of the time - and that number is growing since May, as leagues return and regular testing is implemented. rocketswire.usatoday.com/2020/07/22/rus…
Read 9 tweets

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