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Jul 26, 2021 20 tweets 8 min read Twitter logo Read on Twitter
Covid (@UCSF) Chronicles, Day 495

When I began my tweets 494d ago, it was before we had reliable local, US, or world data. So I focused on data from @UCSFHospitals. Today, we’re awash in data, yet I find my hospital's data still provides a unique lens into our situation. (1/20)
So today, a few data points from @UCSF, with my interpretation. They reinforce the case that the combo of Delta & relaxed behavior is leading to a powerful & worrisome upsurge that requires a change in approach. I knew things were bad, but it’s even worse than I thought. (2/20)
What’s particularly noteworthy about @UCSF experience is that it’s in a city w/ the nation’s highest vax rate. And cases are rising fast in our employees, of whom 93% are vaxxed. (Special thanks to Ralph Gonzales, Bob Kosnik & @SaraMurrayMD for some of the data.) Here goes:(3/20)
Let’s start w/ context: in SF, 69% of all people (76% >age 12) are fully vaccinated. (Vs CA, 52% of population; U.S. 50%.) So the surge in SF is especially sobering, since it indicates that we’ll need an immunity rate far higher than 70-75% to achieve “local” herd immunity.(4/20)
Let's look at hospitalizations. On June 1, we had one Covid patient in our ~700-bed @UCSFHospitals (we never quite got to zero); none were in the ICU.

Today we have 28 hospitalized pts @UCSFHospitals: 15 on the floor & 13 in the ICU (7 on vents). A staggering increase. (5/20) Image
I don’t have the vaccinated/unvaxxed breakdown for today's census, but it’s been running >90% unvaxxed in recent wks. When we do see vaccinated patients in the hospital, many are immunocompromised (a group in which vaccine’s effect is attenuated – we need a new approach). (6/20)
My interpretation: even in a city with very high vaccination levels, serious cases have skyrocketed, mostly in unvaccinated people. Now think about what will happen in a region in which 60-70% of the population is unvaccinated, not SF’s 25-30%. Really scary stuff. (7/20)
In April, I wrote @washingtonpost that “this is the most dangerous moment to be unvaccinated.”….
I was wrong – now is even MORE dangerous since Delta has taken over, caution's been thrown to the wind, and there’s far more virus around. (8/20)
How much virus is around? Since early in the pandemic, I’ve used a piece of data available @UCSF (not publicly) to estimate the chances that a person who feels well in SF is carrying the virus. It’s our “asymptomatic test positivity rate” and it comes from the fact … (9/20)
… that we test all our hospitalized & ED patients who have no Covid symptoms, as well as people undergoing surgeries or procedures like cardiac caths. That fraction was as low as about 0.1% in early June – which was pretty reassuring – it meant that the chances that…(10/20)
… a person near you in a SF store had asymptomatic Covid was ~1-in-1000.

Today, it’s 2.14%! So now that asymptomatic person has a ~1-in-50 chance of being positive. (And this % may be an underestimate since our pts are older than avg, a group with a higher vax rate). (11/20) Image
My interpretation: the risk of getting Covid is related to your vax status, whether you're taking steps to lower risk (masking, etc), & whether you’re exposed to the virus. Even in highly vaccinated SF, the odds of being exposed have gone up ~ 20-fold since June 1. (12/20)
The point's been made that, if everybody’s vaccinated, all infections will be in vaccinated people (even if vax efficacy stays high). Among @UCSF students/employees, we’re not at 100% but we’re close: 32,550 of our 35,018 people (93%) are vaccinated. (Mandate starts 9/1.) (13/20)
Given this vax rate, it shouldn’t surprise that 83% (77/93) of our July cases are in vaccinated folks. This DOESN’T mean vax isn't working – calculated efficacy from these data is 82%. We’d expect 422 cases in our vaccinated population, not 77, if the vaccine didn’t work. (14/20) Image
At least @UCSF, we see no evidence that efficacy is waning: no case uptick in those vaxxed in Dec-Jan vs. more recently. And the vaccines are still >90% effective in preventing severe illness: only 1 these 77 breakthrough infections required a (brief) hospitalization. (15/20)
(This always raises the question of why I, as a vaccinated person, still don't want to get a breakthrough case of Covid. If you're interested, I answered that one here:… (16/20)
Taken together, it’s clear that – even in highly vaccinated SF; it's also a city in which people remained pretty careful despite relaxed rules – we're experiencing a unmistakable surge. The vaccines work great, but, as we now appreciate, they don’t prevent all infections. (17/20)
Even w/ surge, we’re not overwhelmed @UCSF, thanks to vaccines. Scary to consider regions where vulnerable % is much higher. I’m glad the U.S. is finally seeing an uptick in vaccination, but it won’t help for a month (since vax efficacy of dose 1 against Delta is so low).(18/20)
As @DrLeanaWen convincingly argued @washingtonpost, it's time to add back restrictions, esp. indoor masking.…
As for me, it’s back to double-masks indoors & N95s on planes. And sadly, that’s it for indoor dining for a while. None of this pleases me.(19/20)
Along with renewed restrictions, it’s clear that gentle persuasion did not achieve the vax rate we need to defeat Covid. Yes, the politics are hard, but dying is worse, as is re-tanking the economy. It’s time for vaccine mandates – nothing else gets us where we need to go.(20/20)

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More from @Bob_Wachter

May 23
Covid (@UCSF) Chronicles, Day 1161
With the Pub Health Emergency over, it's a good time to update you on my view of Covid & my current approach to Covid behavior – which is now based on 2 principles:
1) Is the risk worth it?
2) Can I live w/ the behavior for the long haul? (1/25)
First, let’s review today's situation. Since Omicron's emergence in 11/21, the biggest surprise has been the absence of surprises. Yes, we’ve seen a few variants that led to mild surges, but we haven’t had to interrogate our Greek dictionary for a new letter for 18 months. (2/25)
mRNAs still work great in preventing severe infection, and Paxlovid, home tests, & ventilation still work well too. Long Covid remains a concern, but we know that both vax & Pax lower its frequency, that most (though definitely not all) folks… (3/25)…
Read 25 tweets
Feb 17
Important @TheLancet systematic review finds Covid infection confers robust & long-lasting (good at 40 weeks) protection vs both symptomatic & severe Covid infection.(Weaker w/ Omicron, but still good.)…
How will results influence my behavior/thinking?(1/7)
a) I've been considering a Covid infection to be the equivalent of a booster in terms of protection against reinfection & severe disease (hospitalization/death). These study results indicate that it is at least that good, maybe even a bit better... (2/7)
b) We've been headscratching about why XBB variant didn't cause more of a surge, despite low uptake of the bivalent booster. It may be that immunity from all those 2022 Omicron infections kept it at bay (that's informed speculation – Lancet study ended before XBB spike)... (3/7)
Read 7 tweets
Jan 19
Covid (@UCSF) Chronicles, Day 1038
Some folks continue asking what I'm doing viz Covid behavior...
Answer: I'm changing my behavior. In the Bay Area, I'm now OK with indoor dining & removing my mask for small group gatherings.
I haven't changed, the risk has. Here's how: (1/25)
Specifically, I haven't changed my perspective on balancing prudent caution with everyone's (including my) desire for "normal."
But, in the Bay Area at least, the Covid risk has come down considerably, and, by my way of thinking, this allows for a more permissive approach.(2/25)
Where I'm coming from:
1) I'm 65 & haven't had Covid
2) I want to live as fully as I can, but am comfortable taking reasonable steps to avoid infection
3) I'm fully vaxxed & had bivalent in Sept
4) My main fear is Long Covid, which I peg at ~5% probability per Covid case. (3/25)
Read 25 tweets
Dec 27, 2022
I appreciate all (or, at least most) of the feedback on yesterday’s post regarding how I make decisions about Covid risks and mitigations, including my 50% Rule.
A brief follow-up thread today, with a few additional thoughts and responses: (1/12)
a) First, of course we’re entering year 4 (!) of Covid (I mistakenly said year 3 in yesterday's first tweet). Sorry.
I was hoping that by now Twitter would have added an edit function, but the new management seems focused on other changes. Hopefully at some point. (2/12)
b) A few folks asked how masking fits into my risk mitigation algorithm.
Just as I’m comfortable doing anything OUTSIDE without a mask, I’m OK in ALL indoor spaces – incl. crowded theaters, subways, etc. – wearing a KN95. I’m also OK removing my mask briefly to eat/drink. (3/12)
Read 12 tweets
Dec 25, 2022
Covid (@UCSF) Chronicles, Day 1013
As we enter Covid Year 3, it’s clear we’ll be in our current predicament for the foreseeable future. This means we all need to find our own method to weigh & mitigate risks.
Today I’ll describe my “50% Rule” & how it governs my choices. (1/25)
All of us make risk choices daily, without much thought. What is the chance of rain above which I’ll bring an umbrella? Do I buy flood or earthquake insurance? Do I take a statin for my cholesterol? In making these choices, it’s rare there’s an unambiguously “right” answer.(2/25)
Instead, we weigh the odds & badness of the thing we’re trying to avoid; how unpleasant, risky, & expensive the mitigation is; & our own risk tolerance. Since the cognitive burden of doing this for myriad choices daily is onerous, we all develop rules of thumb to guide us. (3/25)
Read 25 tweets
Dec 19, 2022
Covid (@UCSF) Chronicles, Day 1006 (!)
There’s an awful lot of Covid confusion & misinformation out there, particularly around these three topics: masks, vaccines, and home tests. Let’s look at them in today's thread. (1/24)
To start, these statements are correct:
• Wearing the wrong mask, or wearing a mask incorrectly, doesn’t work
• Vaccination/boosters don’t work as well as they used to in preventing infection
• Home tests yield more false negative results than they used to.
But these statements are unambiguously wrong:
• Masks don’t work
• Vaccines/boosts don’t work
• Home tests don’t work
This is confusing enough that it’s an easy mark for those who want to spread misinformation. Here’s how I interpret the science to inform my decisions: (3/24)
Read 24 tweets

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