Bob Wachter Profile picture
Chair, UCSF Dept of Medicine. Career: What happens when a poli sci major becomes an academic physician. Author: "The Digital Doctor". Hubby/Dad/Golfer.
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Feb 17 7 tweets 2 min read
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)
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)
Dec 27, 2022 12 tweets 3 min read
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)
Dec 25, 2022 25 tweets 6 min read
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)
Dec 19, 2022 24 tweets 6 min read
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.
Nov 24, 2022 25 tweets 6 min read
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)
Nov 1, 2022 25 tweets 8 min read
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
Oct 20, 2022 25 tweets 6 min read
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)
Sep 18, 2022 25 tweets 7 min read
Covid (@UCSF) Chronicles, Day 915
As I hoped , cases in the U.S. have dropped steadily. Up until now, I’ve avoided indoor dining and worn a mask in all crowded indoor spaces. I’m now ready to eat indoors & (selectively) remove the mask. Here’s why: (1/25) As I said recently, my threshold to liberalize my behavior is <5 cases/100K/d in my region. (After accounting for home tests, 5/100K/d is really ~25/100K/d.) U.S. is now at 19, CA is at 12, & SF is at 6 (& fell 64% in past 2 wks). Find your # here:… (2/25)
Aug 28, 2022 25 tweets 7 min read
I’m not doing indoor dining, and I still wear a mask in crowded indoor spaces. While most in US have chosen to be less careful, in this 🧵 I’ll review the logic & math behind my decisions, hoping that some of you will find them useful in navigating today’s Covid landscape. (1/25) Here’s my bottom line (in case this 🧵is TL;DR):
I’ll begin eating inside and removing my mask in most indoor spaces when the local reported case rate falls below 5/100,000/day.

You can find your local rate of cases/100K/day here @nytimes:… (2/25)
Aug 12, 2022 5 tweets 3 min read
Quick 🧵to update SF Covid situation:
If you’re still being careful in SF (as I am), good news is that cases are down by ~50% in last 2 months, now 244 cases/day, down from peak of 537 (Fig L). As usual, hospitalizations lagging (now 117), but starting to trend down (R). (1/4) ImageImage @UCSFHospitals: 36 pts (6 ICU; ~50/50 “for” vs “with" Covid – Fig L). ⬇~30% in 2 mths; ⬇80% from Jan peak. Asymptomatic test pos. rate=3.6% (R); was ~6% 2 mths ago.
At 3.6%, in group of 20 asymptomatic folks, 52% would test pos – still pretty risky to unmask in big group.(2/4) ImageImage
Aug 3, 2022 25 tweets 5 min read
Making decisions about how cautious (or not) to be w/ Covid remains challenging. In this 🧵, I’ll describe my current approach.
For me, with today's #'s, I find there's only 1 tough call, though it’s clear that most folks disagree – they’ve ditched their masks & moved on. (1/25) I don't criticize anyone’s choice to be less careful. For many people, the value of "normal" & ditching the mask outweighs their perceived risk of, and from, getting infected – particularly now that the risk of a severe case (in vaccinated/boosted people!) is very low. (2/25)
Jul 21, 2022 13 tweets 4 min read
Few quick thoughts re: @POTUS's Covid:
1) Not clear where he got it – he returned from Middle East ~3 days before test +, so probably last day of trip or flight home. Flying is low, not zero, risk, particularly if people weren't wearing masks. (1/13) 2) BA.5 is so transmissible that precautions that worked before may not prevent infection today. It seems like most of the country has "moved on", but if you're still trying to dodge the virus (as I am), need to up your game (ie, KN95 rather than surgical mask). (2/13)
Jul 4, 2022 25 tweets 8 min read
Covid (@UCSF) Chronicles, Day 838
The die is now cast: BA.5 is destined to be our dominant virus.
In today’s 🧵I discuss the implications on the course of the pandemic, and how to think about responding.
(I use “BA.5” & not “BA.4/5” since BA.5 is poised to outrun BA.4.). (1/25) For the science & epi of BA.5, I encourage you to read @EricTopol’s terrific @SubstackInc review.

We’ve now gotten used to Omicron sub-variants – each about 20% more infectious than the prior one – and so it’s easy to be lulled into thinking… (2/25)
Jun 13, 2022 25 tweets 7 min read
Covid (@UCSF) Chronicles, Day 848
It’s been a few weeks since my last update – the flow of Covid news & research has slowed a bit. But there’s still plenty of questions that come up, so in this🧵I’ll answer a few that I get asked commonly, including how my wife is doing. (1/25) Many people ask how my wife @katiehafner fared after her Covid case – we truly appreciate the concern.
The answer is: not great. Now 5 weeks post-infection, Katie has pretty bad fatigue, some brain fog, & periodic headaches. So, according to the most common definition of…(2/25)
May 24, 2022 25 tweets 7 min read
I was asked by a reporter today if I’d take Paxlovid if I had Covid. Last month, this would have been easy: as a 64-year-old person w/ asthma, the answer was an unequivocal YES.
Today, it’s a closer call – in this🧵I’ll lay out the reasons why, and then give you my answer.(1/25) First, an update on my wife @katiehafner's Paxlovid rebound:
Katie finally tested negative yesterday, so her chronology is:
Pos for 8 days
Neg for 4 days
Pos for 5 days
Now negative & feeling better. (Hopefully it'll stay that way; I haven’t heard of double rebounds). (2/25)
May 19, 2022 13 tweets 4 min read
We're hearing lots of reports of Paxlovid rebound, but there are no good data about prevalence. Yesterday I polled my followers to learn more.

The results (next tweet) are striking. (Of course, keep in mind caveats regarding on-line polling results.)(1/13) As of now, there've been 4846 responses. 93% either didn’t have Covid recently or hadn’t taken Pax.
Of the ~350 respondents who HAD taken Paxlovid for Covid, ~46% said they experienced rebound (new symptoms plus a test that went from – to +), vs. 54% who said they did not.(2/13) Image
May 18, 2022 25 tweets 6 min read
If you follow me, you know that my wife @katiehafner had Covid last week, took Paxlovid, & is now testing negative.
In this 🧵(w/ a few polls to see your thoughts), I’ll discuss what to do in the post-Covid period, in light of the latest Covid curveball, Paxlovid rebound. (1/25) To recap: Katie taught at a science writer’s workshop in Sante Fe, May 2-6. There were 50 attendees. Vax required; testing not. Masks were optional. Katie masked during sessions, but ate with the group indoors multiple times. Her symptoms began on Saturday May 7, and she… (2/25)
May 9, 2022 23 tweets 5 min read
The latest Omicron variant (BA.2.12.1) is the most infectious yet, & it’s snagging tons of people who have avoided Covid for > 2 years. It’s hitting close to home for me, so tonight’s 🧵is about that…with a few poll questions to see how your thinking lines up with mine. (1/23) My wife, @katiehafner, like me a healthy 64-year-old, has been quite careful but – with my encouragement – has re-engaged with the world, confident that her 2 vaccine shots and 2 boosters will protect her from serious illness, and reconciled to the fact that Covid may not…(2/23)
May 4, 2022 25 tweets 6 min read
The steady drumbeat of cases, coupled w/ CDC’s finding that 60% of Americans have had Covid…, naturally raises the inevitability question: Are we all destined to get Covid? And, is it worth remaining careful?
I’ll address these questions in this 🧵. (1/25) It can certainly FEEL inevitable – especially when every day brings news of Covid+ friends & family, including many who are vaxxed/boosted & staying careful. Omicron sub-variant BA.2.12.1 is remarkably infectious, leading to a real (& underestimated) ⬆in U.S. cases (Fig). (2/25)
May 2, 2022 4 tweets 2 min read
Covid case numbers less reliable than before (home testing, fewer test sites). Our @UCSF asymptomatic test pos rate (ATPR) remains a good proxy for community prevalence.
Bad news: in last few weeks, ATPR is⬆3-fold, now 3.4%. Implies ~1/30 asymptomatic folks in SF are pos. (1/4) In last mth, SF has become far less mask-y. At this point, if you've decided you're OK getting Covid (which isn't crazy if vaxxed/boosted), then fine to keep mask off in crowded indoor spaces. If you'd prefer to avoid Covid & have become less cautious, it's time to re-think.(2/4)