Let’s talk about the “Swiss cheese model” of combatting the COVID-19 pandemic. This is a classic conceptualization of how to cope with hazards, and it powerfully illustrates several features of what we are facing in the pandemic. #SwissCheeseModel (Image h/t @MackayIM) 1/
What is required to stop the spread of a pathogen like SARS-CoV-2 is achieving some kind of (minimum) threshold level of response sufficient to achieve a deflection in the trajectory of the epidemic, to bring it under control. 2/
A combination of “contact reduction” interventions (eg, school closures, gathering bans) and “transmission reduction” interventions (eg, handwashing, masking) is required. These are “non-pharmaceutical interventions” (NPI), in contrast to things like medicines and vaccines. 3/
But here is the thing: no matter the specific combination of non-pharmaceutical interventions, so long as a certain *threshold* is achieved, the pandemic can be brought to heel. #SwissCheeseModel 4/
As discussed in Apollo’s Arrow (amazon.com/Apollos-Arrow-…), any *combination* of responses may be adequate.

But a person, family, firm, or nation must implement at least some interventions, and they must do more than just one or two! #APOLLOSARROW 5/
In order to stop the spread of SARS-CoV-2 and substantially reduce the risk of the COVID-19 epidemic in a family, firm, or nation, one just needs enough layers of Swiss cheese (in the #SwissCheeseModel), but not necessarily *all* of them. 6/
This also explains how and why different countries have succeeded -- using different combinations of approaches.

In Korea, they relied on masking and testing; in New Zealand, on border closures and contact tracing; in Greece, on gathering bans and school closures. 7/
To be clear, the foregoing countries did more than just those things mentioned. And most countries did various combinations of things. And the timing of implementation is also crucial. 8/
Here are two recent @nature papers assessing the impact of a selection of NPI interventions: nature.com/articles/s4158… & nature.com/articles/s4158…

And also, via @medrxivpreprint, two others: medrxiv.org/content/medrxi… & medrxiv.org/content/medrxi… 9/
This conceptualization also explains why countries and places that do not do enough, that do not have enough layers of Swiss Cheese, wind up with outbreaks. 10/
The recent failure to control COVID-19 in the White House super-spreading event may relate to an over-reliance on testing, without *also* implementing physical distancing, masking, or additional interventions. (For tracking that event as it unfolded: ) 11/
Some "layers" of the Swiss cheese have fewer or smaller holes (are more effective) and are especially helpful when they part of the stack of interventions aimed at stopping SARS-CoV-2 from penetrating the defenses. Being outdoors, testing, and masks are in this category. 12/
This #SwissCheeseModel conceptualization was first introduced by James Reason to discuss failures in complex systems that require coordination of many human and mechanical elements in order to avoid catastrophe (such as in nuclear power and airplane accidents). 13/
A classic application of the #SwissCheeseModel by James Reason to the occurrence of medical error, after the failure of multiple layers of defense, was in this 2000 @bmj_latest paper bmj.com/content/320/72… #socy126 14/

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More from @NAChristakis

12 Oct
Extremely sobering new analysis via my colleagues @LHSummers & @Cutler_econ in @JAMA_current concludes that SARS-CoV-2 is a "$16 Trillion Virus" ja.ma/3diC0U9 1/
The economic impact of the COVID-19 pandemic is huge:
1) $200,000 per family; or
2) 90% of a year’s GDP; or
3) 4 times the output loss of the Great Recession; or
4) 2 times the cost of all wars since 9/11; or
5) roughly the cost of climate change in the next 50 years. 2/
About half the 16 trillion dollar [sic] economic impact of COVID is lost GDP, and the other half is the various health consequences. 3/
Read 4 tweets
2 Oct
POTUS is now reported to have COVID symptoms, which, combined with his other baseline risk factors, is concerning. cnn.com/2020/10/02/pol… Most likely, he will recover, but the medical path is not assured and the political implications are substantial.
POTUS is confirmed to have fever and cough, consistent with *lower* respiratory infection. If hospitalized, this will indicate even greater severity. The coming week will be very indicative of likely path he will take through this serious viral illness.
If he is hospitalized in the coming days (and not simply and truly out of an abundance of caution), POTUS will be facing a roughly 1 in 6 chance of death from COVID19.

If he is intubated, the risk will be higher still.

People to whom he spread the disease may also get sick. 3/
Read 57 tweets
2 Oct
This video, from old work of ours, shows how a respiratory virus spreads across social ties, inexorably, and it illustrates the sort of time course we can expect to occur in a social group like the (mask-less) staff around POTUS. We will hear soon of more cases. 1/
One of the reasons politicians and celebrities contract diseases early in an epidemic, as discussed in #APOLLOSARROW, is precisely that they are often central in social networks, and have many interactions. It's not just that we hear about such people because of their fame. 2/
During past pandemics, including the 1890 and 1918 pandemics, many world leaders contracted infections, as discussed in #APOLLOSARROW (amazon.com/Apollos-Arrow-…). We are seeing this again in 2020, with Johnson, Bolsonaro, and Trump. 3/
Read 6 tweets
21 Sep
Inventing a #COVID19 vaccine is just a first step. For it to make a material difference in the pandemic, we must also manufacture and distribute it, and people must take it (with confidence that it's safe). Let’s talk about the often-overlooked, unsexy problem of DISTRIBUTION. 1/
There are many efforts afoot using diverse biological approaches to develop a vaccine. I think it is likely one will be invented – though how safe and effective it will be, and when it will appear, are still far from certain. 2/
As discussed in #APOLLOSARROW, out on October 27 amazon.com/Apollos-Arrow-…, the many steps necessary before widespread vaccination takes place may mean it does not arrive before we reach herd immunity anyway, in 2022 or so. So a vaccine may not materially shorten the pandemic. 3/
Read 32 tweets
30 Aug
Cool paper by @LHDnets et al shows potential unintended consequences of *inconsistent* #COVID19 NPI policies across jurisdictions.

People moving from place to place can spread #SARSCoV2 to new places as the seek to avoid constraints in their own area. medrxiv.org/content/10.110… 1/
For instance, in March 2020, 10-30% of US churches had increased attendance, even as total number of church visits declined nationally.

People *move* to find open venues, even if it requires long-distance travel. Average distance travelled to churches rose 13% in the period. 2/
Mathematical models reveal that partial measures can often be worse than no measures at all. In the most severe cases, individuals not complying with policies by traveling to neighboring jurisdictions can create epidemics when the outbreak would otherwise have been controlled. 3/
Read 4 tweets
30 Aug
While spontaneous yawning is common across all vertebrate classes, *contagious* yawning is less common and has been observed only in a few species of *social* animals.

But, sweetly, elephants yawn when we do. 1/
A 2018 review of functions of yawning: sciencedirect.com/science/articl…

A 1999 review of *evolution* of yawning: link.springer.com/article/10.100… 2/
Elephants were shown to yawn in 2017. frontiersin.org/articles/10.33… 3/
Read 9 tweets

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