Bob Wachter Profile picture
Jan 19 25 tweets 7 min read
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)
As I've described , this leads me to being comfortable indoors without a mask when the effective case rate is <10/100K/d in my region. This # is based on my own risk tolerance & risk factors. Some people may choose to accept more risk, others less.(4/25)
Because fewer people are testing in general, & more testing is at home, published case rates aren't as useful as they used to be. But trends in case rates are likely to still be meaningful, particularly if they agree with other data sources that are less subject to bias. (5/25)
That's how I approach things: I look at the published case rates in my region, and then look at other data sources less subject to measurement/reporting bias. The latter are:
1) Wastewater
2) Covid hospitalizations
3) Our @UCSFHospitals asymptomatic test positivity rate (6/25)
None of these measures are perfect. Wastewater is a great, unbiased measure of circulating virus trends in a population, but it doesn't really give you a good answer to "What are the chances that a person at my table in a restaurant has Covid and is infectious?" (7/25)
Hospitalizations are influenced by the age of the population, co-morbidities, vaccination rates, as well as the usual, "Is the person hospitalized 'with' vs. 'for' Covid" questions. But hospitalization trends also give a feel for how much Covid is in the region. (8/25)
@UCSFHospitals asymptomatic test + rate has been my go-to # for estimating the likelihood that a person who feels OK in SF has Covid. But it's a bit less reliable than it was since we're no longer testing all pre-op pts – only ones where surgeon or patient requests testing.(9/25)
Yet we're still doing a lot of asymptomatic testing (~300/d), & I'd guess that any bias introduced by voluntary testing might be to push the rate a bit higher – with people who ask for a test being ones who might have a reason to wonder if they're positive. And,... (10/25)
... like many of these data points, even if they're not perfect, the trends offer important insights. So if our asymptomatic test positivity rate is half of what it was last month (as is the case), I would assume there is a significant fall in Covid population prevalence. (11/25)
With all that as background, let's look at the numbers.
Per @nytimes, SF's current case rate is 14/100K/d. But NYT uses a 2-week average, and it's falling fast (down 25% in last 2 weeks). @SF_DPH has us at 99 cases/d (=12/100K/d; Fig), avg'd over 1 week and also falling. (12/25) Image
So it's reasonable to assume that case rate is ~10/100K/d in SF today.
Does that jive with the other, more reliable measures?
Wastewater (SF) is shown below. Again, hard to translate this into quantitative risk, but it supports the premise that there's less virus around. (13/25) Image
Next, hospitalizations @UCSFHospitals. Again, not easy to translate this into risk of, say, indoor dining, but trend line certainly supports the premise that there's less virus around than last month. BTW, our 22 patients in hospital today compares with ~150 in Jan 2022. (14/25) Image
Finally, there's @UCSFHospitals asymptomatic test pos. rate (Fig). It's now 2.4%, down from ~5% in Dec. This implies 1-in-42 asymptomatic folks would test positive. But since it's a PCR, ~half wouldn't be infectious (PCR stays + for ~15-20d; infectious for ~5-10d). So...(15/25) Image
...a 2.4% rate implies ~1-in-100 folks who feel well may be infectious. To me, that's still a reason to prefer outdoor dining over indoor, to add ventilation when feasible, & consider testing before hi-risk gatherings. But it's low enough for me to drop my guard a bit. (16/25)
In Oct-Dec, the additional threats of RSV & flu served as a tiebreaker -- ie, if it was a close call, I'd favor caution since, while the above precautions are to decrease Covid risk, the same practices also help with Flu/RSV. But these two threats have also receded a lot. (17/25)
So there you have it. Based on all of this data and analysis, what am I doing in specific situations?

I'm having dinner indoors w/ wife & kids tonight in SF.
But we're seeing older friends in Palm Springs this weekend: we'll eat outdoors & test before we arrive. Ditto when I visit my 87 year old mom in FL next month (case rate in FL is twice CA's, & going up). (19/25)
Public transit, theaters, other large gatherings:
Plan to wear a mask (always a KN95; why not wear a good mask if you're going to mask?), likely forever. I'm comfortable taking it off briefly to eat on a long flight, but will try to keep it on when I can.(20/25)
Small indoor gatherings:
Poker – I'm now comfy playing with a small, vaccinated group (n=8) without testing. I'll lobby (till they throw me out) to keep the doors/windows open during the game.
I'll do the same with other small indoor gatherings (eg, friends at the house).(21/25)
30 minutes in a crowded Safeway: I'll keep wearing my mask.
Darting into an uncrowded bodega to get ice cream: I probably won't wear it. (Probably shouldn't eat the ice cream either, but that another story.) (22/25)
As always, I'm not telling anybody what they SHOULD do. Perfectly reasonable people have looked at all of these odds (or decided not to) and chosen to live life like it's 2019. Most of them will do just fine – they'll have a higher odds of getting Covid than me, but...(23/25)
.... few will get super sick (particularly if up to date on vax), & most won't get Long Covid (either prolonged symptoms or be victim of elevated long-term risk of stroke, MI, or cognitive decline).
And I have no doubt that there's some joy in getting back to "normal." (24/25)
But I continue to be guided by the current risk, & so I'll continue to follow case rates & other metrics. And, if warranted, I'll re-up my precautions. Just because we're all tired of this doesn't change the risks & thus doesn't change the way I think about managing them.(25/end)

• • •

Missing some Tweet in this thread? You can try to force a refresh

Keep Current with Bob Wachter

Bob Wachter Profile picture

Stay in touch and get notified when new unrolls are available from this author!

Read all threads

This Thread may be Removed Anytime!


Twitter may remove this content at anytime! Save it as PDF for later use!

Try unrolling a thread yourself!

how to unroll video
  1. Follow @ThreadReaderApp to mention us!

  2. From a Twitter thread mention us with a keyword "unroll"
@threadreaderapp unroll

Practice here first or read more on our help page!

More from @Bob_Wachter

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
Nov 24, 2022
Covid (@UCSF) Chronicles, Day 982
Today – my Covid (as well as flu & RSV) plans for the Thanksgiving gathering. I’ll walk you through my current assessment of risks and risk mitigation strategies, and why I’m still being moderately careful. (1/25)
We’re having 12 family and friends over this afternoon. Our plan: while there will be some hanging out inside the house, the bulk of the festivities (including the meal) will be outside. And everybody will rapid test beforehand.
Here’s how we came to this strategy: (2/25)
First, case rates are up moderately, though not as high as I thought they’d be, given that the now-dominant BQ variants look to be fairly immune-evasive. But, for reasons we can’t completely fathom, our overall immunity (from vax & infections) is preventing major surges. (3/25)
Read 25 tweets
Nov 1, 2022
Covid (@UCSF) Chronicles, Day 958
(I'm Still Here Edition)

Today, a brief update on the numbers (TL;DR: they’re reassuringly stable); my take on new studies of the bivalent booster, Long Covid, Paxlovid, & variants; and what I’m doing Covid-wise during this relative lull. (1/25)
Let’s start with numbers. Nationally, Covid cases, hospitalizations, & deaths all remain stable (Fig). The combined effect of more infectious variants & colder weather, along w/ the big drop in masking & the weak uptake of the new booster, is likely to result in a winter… (2/25) Image
…surge. But little evidence it’ll be a big one. (Note CDC no longer shows case forecasts–theirs or others'–due to “low reliability.”)
CDC data shows that BA.5 is now being outpaced by new variants (mostly BQ.1 & BQ.1.1), which seem poised to become the dominant variants. (3/25) Image
Read 25 tweets
Oct 20, 2022
Covid (@UCSF) Chronicles, Day 946
It’s been a while since my last update & now seems like an opportune time. While Covid is still with us, the threat level is fairly low & the last few months offer a window into what our next few years will look like–making it a good time…(1/25)
…to find your behavioral sweet spot. Saying, “I’m not indoor dining now” may imply “I’m not indoor dining ever,” since 23-24 aren't likely to be much safer than now.
On top of that, we’re likely to see a winter surge (modest, I think), so it’s also worth planning for that.(2/25)
Finally, I also think it’s wise for policymakers to shift from emergency mode into a more sustainable stance, as Biden & Newsom have signaled. Covid will remain a real threat – requiring attention & significant investment – but it’s no longer the emergency it once was. (3/25)
Read 25 tweets

Did Thread Reader help you today?

Support us! We are indie developers!

This site is made by just two indie developers on a laptop doing marketing, support and development! Read more about the story.

Become a Premium Member ($3/month or $30/year) and get exclusive features!

Become Premium

Don't want to be a Premium member but still want to support us?

Make a small donation by buying us coffee ($5) or help with server cost ($10)

Donate via Paypal

Or Donate anonymously using crypto!


0xfe58350B80634f60Fa6Dc149a72b4DFbc17D341E copy


3ATGMxNzCUFzxpMCHL5sWSt4DVtS8UqXpi copy

Thank you for your support!

Follow Us on Twitter!