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Lots of media coverage of the striking numbers on @nytimes front page today, based on a preprint from @ColumbiaMSPH ( @Senpei_CU et al), and for good reason. We could have averted 36,000 deaths just by starting the lockdown 1 week earlier! (THREAD) 1/ https://www.nytimes.com/2020/05/20/us/coronavirus-distancing-deaths.html
They give "counterfactuals": what would have happened if we had done something different? There are so many ways to ask that question right now. What if we had started testing sooner? What if we hadn't locked down? What if we had reopened the economy sooner, or later? 
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This is where math comes in! With estimates for how transmission works in a given place, we can play "what if" to explore control strategies, see what we could have done differently, & evaluate consequences of our actions 3/
All models are wrong, but IMO this one does a pretty good job estimating transmission dynamics in every US county & how they depend on movement & testing. Counties are linked by commuting and travel & transmission rates vary by population density and other factors. 4/
This study, and the media coverage, focuses on the negative: what could we have done better if we had heeded the warnings sooner? This is a really important message, and it is sobering as communities begin to plan for opening up. 5/
For what it's worth, we did a counterfactual analysis for Santa Clara County, California (yes, THAT Santa Clara 
) a month ago, but we looked at the BENEFITS of early action. 6/ https://www.medrxiv.org/content/10.1101/2020.05.03.20089078v1
) a month ago, but we looked at the BENEFITS of early action. 6/ https://www.medrxiv.org/content/10.1101/2020.05.03.20089078v1
Unlike NYC, SCC told us to #StayAtHome 
on March 17, when we had only recorded a few deaths. We were the first county in the country to do this (along with 5 other Bay Area counties), based on a really resourceful serosurveillance study by SCC DPH. 
7/ https://www.cdc.gov/mmwr/volumes/69/wr/mm6914e3.htm?s_cid=mm6914e3_w
on March 17, when we had only recorded a few deaths. We were the first county in the country to do this (along with 5 other Bay Area counties), based on a really resourceful serosurveillance study by SCC DPH. 7/ https://www.cdc.gov/mmwr/volumes/69/wr/mm6914e3.htm?s_cid=mm6914e3_w
Even though Santa Clara County also had what is now the first reported COVID-19 death in the US, on Feb 6, we've managed to keep the total deaths down to 138 and reported cases to 2492. Shelter-in-place worked! 
8/ https://www.sccgov.org/sites/covid19/Pages/dashboard.aspx#cases
8/ https://www.sccgov.org/sites/covid19/Pages/dashboard.aspx#cases
R0 was ~3, and we brought it down to ~1 (the threshold btw a virus becoming an epidemic or fading out). So what was the benefit of the early shelter in place? We averted an estimated 95 deaths up to Apr 23: almost exactly the number we had actually observed up to that date. 
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We cut the total deaths in half just by choosing to #StayAtHome one week earlier 
! And that was a month ago--the benefits are even bigger now. Given how early SCC actually enacted shelter in place, we didn't think it could (or should) have been done any earlier. 10/
one week earlier ! And that was a month ago--the benefits are even bigger now. Given how early SCC actually enacted shelter in place, we didn't think it could (or should) have been done any earlier. 10/
But what if we had had access to sufficient testing and were able to test and isolate all symptomatic people by early March? We could have saved an additional 24 of 96 (25%) of the lives that were lost up to 4/22. 11/
To me, this is a story of leadership success at the state and local level, hindered by leadership failure at the national level. 12/
Our key to reopening safely in SCC? Maintain some social distancing as best we can, & test+isolate EVERYONE with symptoms (& their contacts). @SCCgov just announced FREE testing for everyone in who wants it, with 30 testing centers in the county 
13/ https://www.sccgov.org/sites/covid19/Pages/covid19-testing.aspx
13/ https://www.sccgov.org/sites/covid19/Pages/covid19-testing.aspx
Counterfactuals help us understand the impact of our decisions: where we went wrong & how we can do better. We can also see the benefits of social distancing and sound policy decisions, at a time when public trust in decision-makers is critical. /end
