1/ Covid (@UCSF) Chronicles, Day 28
Rock stable @ucsfhospitals, w/ 20 Covid cases, 5 on vents. Even better, ZSFG w/ 28 pts (down 6 from yest!), 11 intubated (down 1). No signs of hospitalization bump from homeless outbreak in SF, though not out of woods for at least a few days
Rock stable @ucsfhospitals, w/ 20 Covid cases, 5 on vents. Even better, ZSFG w/ 28 pts (down 6 from yest!), 11 intubated (down 1). No signs of hospitalization bump from homeless outbreak in SF, though not out of woods for at least a few days
2/ SF also stable: 987 cases, up only 30 cases (L Fig). 15 deaths overall, for case-fatality rate of 1.5% (vs U.S. rate of 4%, NY 5%, MI 6%) bit.ly/2XCsA00 Deaths prob. higher when region is hard-hit. Total hospztns in SF also stable (R Fig); prob will start falling soon
3/ @UCSF rate of + tests remains ~4%, well below CA avg 13%. Today, we ran 70 Covid tests (as of 5pm), & zero were positive! (Fig=@ucsfhospitals dashboard) Yest, 1 pos out of 134 tests. Clearly, few new cases; stable hospital/ICU # s is trailing indicator (since pts stay a while)
4/ @GavinNewsom today on modifying lockdown: bit.ly/3bm3cjb When? GN: “We want to see hospitalizations…& ICU # s peak & start to decline” for couple wks…"1st wk in May, ask me the questn then…but let’s not make the mistake of pulling the plug too early.” V. reasonable
5/ Press loved @nirajs23’s 49ers story; eg @WSJ on.wsj.com/2VcVTVn I liked neighborhood paper @MLNow piece on how @UCSF Grand Rounds (usual crowd ~50 MDs) has become go-to Covid forum bit.ly/34AWMdj 4/9 @YouTube here: bit.ly/2K27T5s Next Grand Rounds 4/16
6/ One interesting Covid-related phenomenon has been general embrace of scientific terms of art: “flattening the curve,” “social distancing,” “PPE." Newest kid on block: “herd immunity.” Worth taking a moment to understand what it means, and why it won’t be our savior (sorry)…
7/ Herd immunity = min fraction of population that's immune to lead an infection to slink away. Of course, if 100% are immune (either via prior infections or universally effective vaccine that all receive), infection will die out. But the number can be <100% to kibosh an epidemic
8/ How? Recall, if each infected person infects <1 persn (lingo: R0 [“R-naught”] <1; now we’re all amateur epidemiologists!), virus dies out. Coronavrs's R0 ~3, meaning that avg pt infects 3 ppl bit.ly/3abEWhY Ergo, exponential growth: 1 case begets 3 begets 9, and so on
9/ Paper (bit.ly/2z2hJ59 & Fig): link between transmission rate & fraction of population that must be immune to get herd immunity. In U.S., avg Covid pt infects 3.29 others -> herd immunity needs 69.6%. (Paper's “Rt”, effective transmission rate, is = R0 when few immune)
10/ Simply put, if 70% of population is immune & I come in contact with 3 people who I might have infected when outbreak began (when no one was immune), I’ll now infect only one (2/3 can't become infected). Voila, new cases begin to fall, and pretty soon we’re in good shape.
11/ Are we close? ‘fraid not. True, w/o antibody testing we’re guessing. Best data prob @ScienceMagazine paper (China): 86% of infections undocumented bit.ly/2Vy5rsZ If right, then NYC’s 110K cases = ~700K actual cases (diagnosed & undiagnosed), still <10% of population
12/ ...and that fraction would be the highest in the U.S., by far. California, with 25K diagnosed cases, might truly have about 150K infected people, or 0.4% of its population. A far cry from the 70% we’d need for herd immunity to be relevant to our near-term future.
13/ One bizarre theory out there: CA has had few cases because many folks were “infected last fall” – and so (says theory) most of us are already immune bit.ly/2RFKqeB Story totally debunked by @trvrb bit.ly/2xuyIww Not worth wasting any more ink on this – wrong
14/ If you're rooting for herd immunity via Covid infectns, we’d need >200M people in U.S. infected to get to ~70% immune. With fatality rate ~4%, that's ~9 million deaths. In other words, herd immunity won’t get us out of our pickle. Yes, root for herd immunity, but via vaccine.
15/ End note: I’ve done ~25 press interviews in 2wks. While I fretted re: doing conservative media (not exactly my politics), my wise wife convinced me “no” would just add to echo chamber. Below: two gracious thank you's – both from R-leaning shows. So there’s that…
Stay safe
Stay safe
A reasonable point that the actual mortality rate of the entire infected population is no doubt closer to 1% than 4% (since the undiagnosed cases are generally less sick). But even at 1%, we’re at ~2M deaths to achieve herd immunity via infections. Still an unattractive strategy.
And, as I pointed out many times, all of this assumes that infection leads to complete immunity, which is currently a hope rather than a certainty.
