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Tonight #DeborahBirx stated that models anticipating large-scale transmission of COVID-19 do not match reality on the ground. Our modeling (done by @StephenKissler based on work with @ctedijanto and @yhgrad and me) is one of the models she is talking about.
We received a request to model dozens of scenarios from the US government at 5pm on Tuesday. We responded to many of these on Wednesday evening, thanks to fast and careful work by @StephenKissler. This was done in good faith in order to help support the USG response.
Modeling the scenario of intense social distancing for a temporary period, followed by a letup, produces predictions of resurgent transmission and large epidemics, with the exact consequences depending on the degree and duration of reduced transmission during social distancing.
Dr. Birx's statements today… indicated that "when people start talking about 20% of a population getting infected, it's very scary, but we don't have data that matches that based on our experience."
True. We are near the beginning of the epidemic, with most people still susceptible. China and Korea have suppressed transmission by massive testing, combined in China with far more intense distancing than here and in Korea with significant distancing…
If our social distancing works it is possible we will not just flatten the curve, but get a decline in cases. Under a best-case scenario, we will keep that policy in place long enough to get down to very, very few cases domestically.
If at the same time we ramp up testing capacity and the ability to trace contacts, in a very best-case scenario, we might conceivably be able to turn to a Korea- or Singapore-style mix of less intense distancing combined with super-intense contact tracing, isolation, quarantine
That will not be easy with this virus as our @CCDD_HSPH analysis has shown… but as some (mainly island) countries have shown, it may be just possible. We should do everything we can to reach for this goal, even if it is unattainable.
But here's why it is a best-case, likely unattainable scenario. 1) We have not proven that US-style social distancing can produce R_effective<1 (declining case numbers). On this I'm hopeful, but it's a hope not a fact.
2) we remain woefully behind on testing capacity, especially in many parts of the country. Like a forest fire, intense control in one place fails if there are sparks from other places. We must strengthen the weak links. But test reagents, swabs, PPE remain in short supply.
Solving the testing problems will not be easy, despite heroic local and state efforts to make up for the feckless federal efforts on this front. Supply chains are delicate and it may not be possible to come from behind and establish Korea-level testing capacity.
3) We have never accomplished contact tracing on the scale that will be necessary -- and again, to keep cases low, we will have to accomplish that everywhere, not just some places.
4) If we manage all of that, there will still be a world of COVID-19 transmission throwing sparks back at us. Like China today… we will be in a long-term effort to prevent these sparks from starting new chains of transmission.
The sparks from abroad won't be stopped by detection at the border; we don't do that too well as we showed empirically… and others @cmmid_lshtm showed theoretically…
So the scenario Dr. Birx is "assuring" us about is one in which we somehow escape Italy's problem of overloaded healthcare system despite the fact that social distancing is not really happening in large parts of the US…
That is unlikely. Then the rosy scenario assumes we get to minimal numbers of cases everywhere, develop and maintain testing and tracing capacity, execute well on it, don't miss imported cases that spark new chains of transmission, and somehow maintain this delicate balance...
For the 12-18 months (best case under current models) till a vaccine. I desperately hope she is right, because much suffering will be avoided. But reassurance that this is likely, or even plausible, with the disorganized track record of the US response, is false reassurance.
We should work our hardest to create the conditions to make the scenarios being described here (one bad wave, contained by social distancing, and we're down to a point of controllable spread) a reality. Doing so will make us better prepared, even if they don't come to pass.
But it would be extremely naive to imagine that they are likely, and what do I know, but it seems like bad politics to "assure" the American people that they will come to pass when so many things could go wrong, any one of which leads to much worse outcomes.
On a simpler level, saying that "facts on the ground" are not consistent with 20% of the population getting infected is really quite deceptive. Likely, no population has 20% yet infected (though we can't be completely sure until serologic testing is widespread).
But this virus has shown in countries around the world that it can spread rapidly, and a small problem can become a big problem -- that is how exponential growth works.
It is a fundamental scientific error to take the current success of containment in some places as a sign that permanent containment is possible. We should work to make it possible, but 1918 flu and, frankly, the germ theory of disease show that containment is a temporary victory
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