Bob Wachter Profile picture
May 18, 2021 25 tweets 6 min read Twitter logo Read on Twitter
1/ Covid @UCSF Chronicles, Day 426

I’ve been letting the new CDC guidelines marinate for a few days, getting over the shock of seeing an agency that’s usually a trailing indicator so “out there.” I tried, but I can’t talk myself out of seeing the new recs as too far, too fast.
2/ This afternoon, my state of California rendered the same judgment, delaying the lifting of indoor masking requirements until June 15th. The extra month will make a big difference – it’ll give folks who just got access to vaccines in April & May time to get fully vaccinated…
3/ … and also afford 12-15 year-olds a chance to be vaccinated. It also means – if the projections are right – that there will be far less virus in the air by mid-June, which will make indoor activities safer, even if some unvaccinated people take off their masks.
4/ Here’s my take on the CDC guidelines: If we could trust everyone to follow the rules – especially the one that says unvaxxed people stay masked inside – then the guidelines would be OK. I’m happy to be indoors w/ un-masked vaccinated people, and w/ masked unvaccinated people.
5/ But we can’t count on that happening.

While I can’t prove it, I have to believe that more than a few folks who've chosen not to be vaccinated will also be ones who reads the “no mask needed…” part of the CDC document & stop before the “…unless you’re unvaccinated” part.
6/ When WOULD the relaxed CDC rules make sense? If a trustworthy system of immunity passports was in place to ensure that unvaccinated people either weren’t allowed in or were required to mask, that’d be fine. But, while some businesses & schools are going there, the fact that…
7/…the federal govt. has decided that vaccine passports are too hot to handle means that it won’t be a widespread practice.

And, given the ease of purchasing forged CDC cards, even a system of “carding” vaccine status will be untrustworthy, 2021’s version of pandemic theater.
8/ Rather than vaccine passports, CDC could have linked lifting restrictions to very low state or regional case (or high vaccination) rates. The rationale: in a place w/ very little Covid floating around, it wouldn’t matter much if some unvaccinated folks were unmasked indoors.
9/ Moreover, a strategy of linking relaxed mask requirements to low case or high vaccination rates would have offered a community incentive for vaccination – an incentive that the new CDC rules give lip service to but really don’t do very much to stimulate.
10/ What kind of thresholds would be reasonable? Probably ones near CA's current low rates, such as avg. new cases/day <5/100K (CA is currently 3.2/100K) & test pos. rate <1% (CA is 0.9%).

We could also use >50% fully vaccinated (CA is currently 38%, matching the U.S. average).
11/ You could argue that CA is close to these case thresholds. Still, I’m glad they delayed till June. This'll allow us to increase vaccination rates & drive case rates down further. Unlike CDC’s Big Reveal this week, it also gives CA some time to get prepared for the change…
12/ … including messaging the importance of vaccination, and giving businesses and schools time to get ready to adapt the new world. The delay also creates an incentive for more folks to get vaccinated (since presumably we’d push back the date if case rates start going up).
13/ (Speaking of messaging, I’m told by top leaders of SF, CA, & the feds that cities, states & even the White House had little advance notice of the CDC’s decision to relax the standards. Even those who agree with the guidelines were surprised by the weak communication plan.)
14/ The folks at CDC are smart, evidence-based, & (in 2021) relatively free from political interference. Why did they make the change? I’m guessing that they came to believe that the new guidelines would increase the rate of vaccination by a few percent, and that the cases…
15/ …averted from additional vaccinations would save more lives than cases caused by mask-less unvaccinated people infecting themselves or others. Perhaps so. It’s hard to Monday morning quarterback without access to all of CDC’s intel. But from where I sit, telling people…
16/ …that they can go unmasked indoors in states w/ still-high case rates (Colorado’s rate of 22 cases/d/100K is 6x CA’s) & low vaccine rates is awfully risky. And if there ARE surges (not impossible in low-vax states), it’ll be brutally hard to reinstate the old masking rules.
17/ Good news: even in states w/ relaxed requirements, you can make your own choices! Here’s my thinking on this, based on fact that – while I’m fully vaxxed & thus 99.9% protected against getting very sick and dying – we are seeing breakthrough cases (Exhibit A: NY Yankees)…
18/…and I still don’t want to get Covid if I can avoid it. (Why not: I could be the rare person who gets very sick, & we can’t say for sure yet if mild Covid in a vaccinated person can lead to Long Covid).

So I still avoid elective activities that, to me, create undue risk.
19/ I’ll go mask-less indoors under 3 conditions:

1) I'm sure that everyone there is vaccinated, OR
2) If unvaxxed people are there, I’m sure they’re all masked, OR
3) The local Covid rate is so low that even an unvaxxed unmasked person is very unlikely to have active Covid.
20/ Re #3, let's take SF as an example of a low-prevalence place. Avg. of 21 cases/d (2.4 cases/d/100K), test + rate 0.6%. 53% of city is fully vaccinated. @UCSF, asymptomatic test pos. rate is 0.4%, or 1/250 – my shortcut for the chance that a guy near me @Starbucks has Covid.
21/ But keep in mind that this asymptomatic test positivity rate is now comprised mostly of vaccinated people. I have no way to know the rate in unvaccinated people, but it must be higher. 1% is likely a fair guess, which would mean that an unmasked, unvaccinated person in SF…
22/ …has a ~1 in 100 chance of having Covid. Would I want to be chatting w/ them, indoors without masks? What if they're coughing? What if I was immunocompromised? What about 2 unvaccinated & unmasked people in loud conversation?

I want "normal" too, but it seems too risky.
23/ As vax rates go up & case rates come down, Covid prevalence should fall more & several good things will happen. First, the chances of encountering an unvaccinated person (including a kid) will fall. Second, the chances that an unvaccinated person has Covid will also fall.
24/ And third, maybe we’ll come up with a workable vaccine authentication system to allow us to be confident that everybody inside is vaccinated, or that all unvaccinated people inside are wearing masks. (This scenario strikes me as the least likely – logistically & politically.)
25/ CDC's been great in '21, but on this one they declared victory too early.

For now, whether you live in CA or not, I'd recommend you keep the mask on for another month or so while more folks get vaccinated. We'll get there, but let's not rush it too much.

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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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