A brief San Francisco update. As always, SF is a key test case since it's so highly vaxxed (81% of people w/ ≥ 2 shots) & most still follow public health recs (incl. masking). Nevertheless, we see skyrocketing cases; hospitalizations more modest but starting to tick up.(1/12)
Let's look @UCSFHospitals first. Test positivity rates continue to climb, though if you squint you might see a hint of a plateau. As always, my key # is the asymptomatic test pos. rate, now 7d avg of 8.27% – implying 1 in 12 people in SF without Covid symptoms have Covid.(2/12) Image
With that prevalence, you have to assume that everybody you come in contact with might have Covid.(Cities experiencing greater surges probably have even higher asymptomatic %.)
This is why I haven't been too critical of the CDC's 5d isolation guideline – the risk of...(3/12)
...catching Covid from someone who is carrying it & doesn't know it (& likely isn't masked) is probably no higher than from someone who just had Covid, is on day 6, feels fine, & is masked. Yes, I'd prefer they have a neg. rapid test, but if they're masked they're...(4/12)
... probably no more of a threat than lots of other folks.
Anyway, let's turn to @UCSFHospitals. As I predicted last wk, w/ so much Covid around we were bound to see a hospital surge, and we're now starting to see one: up to 33 pts: 27 on the floor, 6 in ICU. That's up...(5/12) Image
...from ~20 (13 floor, 7 ICU) 10d ago. Given our asymptomatic test positivity rate, at least a few of these are likely pts admitted for other things ("incidental Covid") rather than who are sick FROM Covid, but not all of them – this is real bump. Even so, it's still...(6/12)
...much lower than one would have expected from prior case (see below for SF #'s) & test positivity surges of this magnitude. It says to me that if even in highly vaxxed SF, our hospitals will be stretched. Hospitals in cities w/ lower vax rates are likely to be hammered.(7/12)
Remember that the increase in hospitalized patients is on top of lots of MDs/RNs/other workers out sick. Also, even with no Covid, nearly all hospitals run very full in the winter (with flu & other stuff), so additional volume on top of that can easily exceed our capacity.(8/12)
Let's turn to SF – the case curve continues to head straight north, with no sign of abating. Here you see that it's up 10-fold in a few wks, & this # of 495/d understates the magnitude of the surge for several reasons: 1) there's a lag (it's from a few days ago); 2) with...(9/12) Image
... a slope like this, a 7d average markedly understates what's happening today; & 3) it's missing tons of positive cases that were diagnosed via rapid tests & not reported.
But even so, it's breathtaking. Is it translating into hospitalizations? The answer is mostly...(10/12)
no, with a caveat: @SF_DPH hospitalization data have a 4d reporting lag. So our @UCSFHospitals uptick (no lag) likely predicts a general uptick in SF; I expect we'll start seeing this in the next 1-2 days.
But even when we do, it's still relatively mild. With cases in...(11/12)
... South Africa falling rapidly after 4-6 weeks, it seems like a highly vaccinated city like SF will be able to survive a similarly short surge without being overwhelmed. In less vaccinated (& mask-y) cities/regions, I'd be far more apprehensive.(12/end) nytimes.com/2021/12/30/wor…

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More from @Bob_Wachter

29 Dec 21
My latest tweets have mostly been bad news, which saddens me, particularly during holiday season.
Today I’ll take you to my Happy Place, with some thoughts on why we could be in good shape – and maybe even great shape – in 6-8 weeks.

A 🧵(1/24)
Let’s start by agreeing that the current state is awful, and likely to get worse. Case rates are skyrocketing (Fig L), hospitalizations are going up fast (but not nearly as fast as cases; R), it feels like everybody's infected or recently exposed, & there are shortages of…(2/24)
…key tools, including testing (both PCR & antigen) & therapies (mostly Sotrovimab [the monoclonal Ab that works vs. Omicron] & Paxlovid, the Pfizer oral antiviral with outstanding efficacy in preventing serious illness in outpatients with Covid).(3/24)
Read 24 tweets
28 Dec 21
Today's update on SF/@UCSF numbers. Bottom line –huge increase in cases & test positivity. Hospitalizations still pretty benign (though early signs of an uptick). Most remarkable stat is our asymptomatic test positivity rate (ATPR) @UCSFHospitals – now ~7%, or ~1-in-14.(1/16)
You'll recall that ATPR is fraction of pts getting care (hospitalization, procedure) @UCSFHospitals who we test for Covid routinely, even tho they have no symptoms. I use this as a rough approximation of the prevalence of Covid in Bay Area people who have no Covid symptoms.(2/16)
The ATPR was as low as 1/500 (0.2%) a few mths ago. Today, our 7d ATPR is 6.9%, and last 3 days it's ~8% (going up fast).
If its 8%, it means 1-in-12 people in SF who feel fine would test positive for Covid.(Not all would be in their infectious period, but most would be.)(3/16)
Read 16 tweets
28 Dec 21
There are so many Omicron #'s floating around, it’s overwhelming. In today’s 🧵,I’ll try to simplify things with a couple of rules-of-thumb that I’ve found useful. I’ll be interested in hearing if this helps or confuses more – it might hinge on whether you’re a chess fan.(1/25)
Chess? We’ll get to that in a bit. For several of the big picture Omicron issues, my go-to is not a chess board, but rather the Number 2.
Why 2? Because many of Omicron’s key variables are either just about twice, or approximately half, of what they were with Delta.(2/25)
Two key variables for which “2” is a useful rule-of-thumb:
a) How much more infectious is Omicron than Delta? About twice. (And Delta was about twice as infectious as Alpha was.)
b) How much less serious (measured by hospitalizations) is Omicron than Delta? About half. (3/25)
Read 25 tweets
24 Dec 21
Covid (@UCSF) Chronicles, Day 647 (!)
I haven’t done a San Francisco update for a while. Now seems like a good time, since SF – the most vaxxed big city in the U.S. – may offer lessons for the nation about how an Omicron surge is influenced by high vax (& masking) rates.(1/25)
Bottom line is that some normally-scary numbers (surging cases & test positivity %) haven’t led to big jumps in hospitalizations. The big question: is it still too early to tell, or is this the hoped-for case–hospitalization dissociation at play? I’m going with the latter.(2/25)
Let’s start w/ SF before focusing @UCSFHospitals. Clearly SF is seeing a big surge in cases: ~250 cases per day (7-day daily average is 161; this lags due to the steep uptick), up from avg of 45/d in late Nov. (Figure). So about a 5-fold rise in recent weeks. Concerning. (3/25)
Read 27 tweets
22 Dec 21
This thing has rapidly become the world’s exasperating good news/bad news story. If your head isn’t spinning, you’re not paying attention.

A 🧵on my take on both the good news & the bad, with an emphasis on the things that have changed in the past few days... or minutes.(1/25)
Bad news: Omicron has exploded in the U.S., weeks before we thought it would. As recently as 2 weeks ago, most experts thought this would be a January issue, not a December one. The rapid uptick nationally, particularly in cities like NYC, Miami, & Houston, is jaw-dropping.(2/25)
Even here in SF, the nation’s most vaccinated (and likely boosted) city – and a city where masking is still the norm – we’re now seeing the familiar northward-facing curve (Figure). It’s now clear that no place in the U.S. will be spared a direct hit from Omicron.(3/25)
Read 25 tweets
21 Dec 21
FINALLY, real data on Omicron's severity – from So. Africa & Australia, summarized in threads from @jburnmurdoch & @andrewlilley_au:

Bottom line from these preliminary studies: looks like Omi's per case hospitalization rate ...(1/4)
... is ⬇50-70% compared w/ Delta's. But once in hospital, studies find similar risk of "severe disease" (eg, ICU admit). Impact on death rates? Too soon to say.
Findings are good news overall (equal severity would be awful), though need more data to be sure – the stakes...(2/4)
are just too high. The studies don't tell us if the lower case-hospitalization rate is due to a ⬇in the inherent virulence of Omicron, vs. the impact of immunity from vaccines or past Covid.
Your friendly reminder that we'll likely see case rates that rise by more... (3/4)
Read 4 tweets

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