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THREAD re the "everybody's-got-it" school of covid truthery, which my story this wk in @TheEconomist https://www.economist.com/graphic-detail/2020/04/11/why-a-study-showing-that-covid-19-is-everywhere-is-good-news, based on study by @inschool4life & @Alex_Washburne, supports. Most impt pt is that these results do NOT mean we should end/loosen lockdowns now/soon. 1/n
By now, every1 following this knows that only a minority of people w/ covid-19 are getting tested, & that a substantial share have mild or totally asymptomatic cases. The official case-fatality rate (CFR), which is deaths divided by CONFIRMED cases, of 6% is obv way too high. 2/n
To estimate infection-fatality rate (IFR), which is deaths divided by total infections, have 2 estimate number of undiagnosed cases. Evidence is dribbling in that it's v hi. A review: 1. Entire pop of Italian town of Vò was tested by Mar 6. 3% infected https://www.independent.co.uk/news/world/europe/coronavirus-vo-euganeo-blanket-testing-veneto-luca-zaia-a9411201.html 3/n
2. Serology on 1/3 of the pop of Italian town of Robbio, found 13-14% w/ antibodies to covid-19, 30x num of confirmed cases https://www.unz.com/isteve/even-a-town-in-northern-italy-is-still-pretty-far-from-herd-immunity. 3. Serology on 1K people around Copenhagen found 2.7% w/ antibodies, despite hi false negative rate https://www.sst.dk/-/media/Udgivelser/2020/Corona/Status-og-strategi/COVID19_Status-6-uge.ashx?la=da&hash=6819E71BFEAAB5ACA55BD6161F38B75F1EB05999 4/n
4. Serology on n=500 in Gangelt, Germany found 14% w/antibodies + 2% w/active virus. Used test w/ >99% specificity, making base-rate fallacy ( http://en.wikipedia.org/wiki/Base_rate_fallacy), where false positives dwarf real ones when true cases are rare, less of a concern. https://www.google.com/amp/s/www.technologyreview.com/2020/04/09/999015/blood-tests-show-15-of-people-are-now-immune-to-covid-19-in-one-town-in-germany/amp 5/n
5. Analysis of deCODE Genetics sample in Iceland finds ~10x undercounting of covid-19 infections, even in country w/ highest testing rate in world (6% of pop already tested). Implies 4-5% of country infected. http://www.igmchicago.org/wp-content/uploads/2020/04/Covid_Iceland_v10.pdf 6/n
6. Aforementioned Silverman/Washburne paper estimates increase from Mar 8-28 in share of Americans contacting doctors about flu-like symptoms w/o having flu, relative to historical baseline, at 7% of population. ( https://www.medrxiv.org/content/10.1101/2020.04.01.20050542v1) 7/n
7. Imperial College researchers, using pure epidemiology based on the number of deaths, estimated 5% infection rate by late March across European countries. https://www.imperial.ac.uk/media/imperial-college/medicine/sph/ide/gida-fellowships/Imperial-College-COVID19-Europe-estimates-and-NPI-impact-30-03-2020.pdf 8/n
8. San Miguel County Colorado (centered on Telluride) is testing the entire pop of 8K. There have been delays w/processing. But 2% either positive or borderline/need followup so far. https://coloradosun.com/2020/04/09/san-miguel-county-telluride-universal-coronavirus-testing 9/n
There's obv yuge uncertainty around these estimates. But the 2 studies on small towns that got slammed w/ covid both came out ~15%; others are all low-mid single digits. By contrast, just 0.1% of Americans & Britons, 0.2% of Italians & 0.3% of Spaniards have tested positive 10/n
So undercounting is prob 10x or more. This has both encouraging & disturbing implications. Good: if we've counted deaths right, IFR is 1/10 of CFR or less. 1/10 of current CFR would be 0.6%. That happens to be near one 0.66% estimate of China's IFR. https://www.medrxiv.org/content/10.1101/2020.03.09.20033357v1 11/n
2nd encouraging consequence is that it puts us a bit closer to eventual herd immunity. If only 0.2% of pop has already had covid-19, then we're 9-10 doubling periods away. If 5% has already had it, we're "only" 7 doubling periods away. 12/n
HOWEVER, remember that IFR has both a numerator and a denominator. We're also under-counting the numerator—covid-19 deaths—albeit prob by a smaller magnitude. Excess mortality in parts of Spain, Italy and France is 2-3x official covid-19 death toll https://www.economist.com/graphic-detail/2020/04/03/covid-19s-death-toll-appears-higher-than-official-figures-suggest 13/n
Moreover, many people now infected haven't died yet, but will. You need to compare deaths today to estimated infections 3-4 weeks ago (depending on reporting lag) to guess at the true share. Recorded US deaths the past few days have been ~50% higher than in previous week 14/n
But let's just explore consequences of a low-ish IFR scenario—say 0.3%, so "just" ~3x flu. What would this mean? First, it means covid-19 spreads v quickly. One new paper on spread in China gets r0 of 5.7, DOUBLE earlier estimates of reproductive num https://wwwnc.cdc.gov/eid/article/26/7/20-0282_article 15/n
Very fast growth means extreme, economically destructive lockdowns are needed to stop explosive spread, and that the % of pop infected needed for herd immunity is higher. For those misguidedly arguing to lift lockdowns now, the "everyone" in "everyone's got it" is relative. 16/n
Just b/c recent data implies we're clos-ER to herd immunity than official case counts show doesn't mean we're actually anywhere CLOSE to herd immunity. If covid-19 has really spread undetected like wildfire, then maybe 10% of the pop has had it—which means that 90% hasn't! 17/n
But if covid-19 were not so bad—maybe somewhat deadlier than the flu, but not a full order of magnitude or worse—then why wouldn't we just treat it like chicken pox, and hope everyone gets it so we get to herd immunity ASAP? 18/n
2 reasons. 1st, low-IFR scenarios presume everyone w/ severe cases gets good supportive care. If hospitals get swamped, doctors have 2 triage & death rate soars, like in Italy. And w/ spread as fast as studies imply, hospitals would def overflow. NY is already close to this. 19/n
2nd, getting 2 herd immunity w/o a vaccine, in a low-IFR, fast-spreading scenario means maybe 80% of pop has 2 b infected. & a 0.3% IFR on 80% of pop means that ~1 in 400 people die—like 800K deaths in the US. There's no way we would or should tolerate that kind of mortality 20/n
So yeah. The vast majority of covid-19 cases are prob undiagnosed, & the disease is prob much less deadly than official CFR. Under extreme assumptions, it could even have similar mortality to flu. The proper response 2 this is what govts are already doing: keeping lockdowns 21/n
in place until the rate of new cases drops enough 4 hospitals to give every1 best possible care, & mass testing becomes available so we can rely on contact tracing to open up in appropriately small increments until we get a vaccine. Even if the IFR were just 0.1%, a world 22/n
in which 80% of people all get a flu-equivalent disease at the same time would be an unimaginable catastrophe. 23/23 cc @kmedved @SlaveaChankova @mlipsitch @CT_Bergstrom @natesilver538 @JDVance1 @DKThomp @PatrickRuffini @karlbykarlsmith @TruthIsMySword @ajkaywriter @zarkadakis
cc @onefinejay @BillAckman @MattTracey13 @benbenchia @J_CD_T @mitchellichtman @SethS_D @AudacityOfHoops @jeremychrysler @jaycaspiankang @basile_sportif @TheToddSchulte @bakerlink @raverbruggen @bdetrick @el_reportero @ghoshworld @alfonslopeztena @claireberlinski @newslambert
