Bob Wachter Profile picture
Jan 15 20 tweets 4 min read
Some folks are a bit confused about why things are likely to be much safer in a month than now – not why virus will peak & fall (we don’t entirely know) but why the risk to individuals will plummet – & with that, why activities that are unsafe now will be much safer then.(1/20🧵)
There are about a dozen factors that go into a risk assessment, and only one of them will fundamentally change: the probability that a person near me is infectious.
Let’s go through the other factors to isolate the one that makes virtually all the difference.(2/20)
Will the virus I'm exposed to next month be the same?

Almost certainly. Omicron's now the dominant (>95%) virus in the U.S. (Fig) and it’s a near-certainty that it will be that way next month.
Given its relative "mildness," I hope that's true in 6 months; time will tell.(3/20) Image
Will the virus have different properties in a month?

Almost certainly not. The current characteristics of Omicron – its high degree of infectiousness, moderate immune escape, and relative “mildness” – will continue to be its M.O., despite small mutations. (4/20)
Will my immunity to Omicron change in a month?

There are 4 things that can change:
1)If you get a (or another) vax, you’ll be more immune. Do it if eligible
2)If you get Omi between now & then, you'll be more immune
3)If you get an illness or begin a med that lowers...(5/20)
...your immunity, you’ll be less immune
4)If nothing happens, your immunity to Omicron won’t change (maybe a little time-based decay)
(Note: I find the evidence that “immune-enhancing” vitamins & health foods make a difference pretty unpersuasive. Cue the Tweetstorm!) (6/20)
Will the chances of me catching Omicron from a given encounter (ie, indoor gathering) change?

Not really, unless the environment changes (restaurant has installed better filters or ventilation). If you’ve lowered your personal protection (today you’d use a mask for a... (7/20)
... given encounter and next month you go mask-less or downgrade your mask from, say, N95 to surgical), this will raise the risk. (Importantly: that's if no other variable changes, but one will... read on.) (8/20)
So what gives? The virus is the same, your immunity is the same, the chances of getting infected from a given encounter much the same.
Yet I predict that I – and most of us – who are trying our best to dodge Omicron now will be more “open” next month. Does that make sense?(9/20)
Yes! It's all about community prevalence – basically the chances that the person next to you at the restaurant, the movie, or the store is infectious w/ Covid. It they're not, your encounter is 100% safe. If they are, your encounter is as risky as it is today. (10/20)
Today, near the Omicron peak, the odds an asymptomatic person has Covid is ~10% in most of U.S. At 10% prevalence, when you enter a room w/ 20 people, there’s an 88% chance that one of them has Covid. Do that enough times without masks and you’re going to get infected. (11/20)
In a month – if cases fall to prior non-surge #'s – the prevalence among asymptomatic people may be more like 0.2% – even in less vaxxed regions, which'll have more people whose immunity came from infection. (They should still get vaxxed for better & longer protection.) (12/20)
0.2% means that the odds of an asymptomatic person having Covid=1-in-500. That room of 20 people: now a 4% chance (1-in-25) that someone's infected. Not zero – you'll still want to be careful if you’re at very high risk. But for most, % is low enough to feel pretty safe. (13/20)
And here's where some other variables kick in. The low probability of being exposed to Covid should be multiplied by the probability that you’ll have a really bad case if you DO catch it. That chance has gone down with Omicron’s relative “mildness,”… (14/20)
… particularly if you’re vaccinated.
And with a low community prevalence, if you do get sick, hospitals won’t be overwhelmed and you’ll be able to get the care you need. That also makes an infection less risky. (15/20)
And tests will be more abundant, so you’ll be able to get diagnosed more quickly. And if you do get Covid & you’re at high risk, you’ll have an easier time getting a med (preferably the Pfizer pill, Paxlovid), which will markedly lower your chance of getting very sick. (16/20)
Yes, the specter of Long Covid (for some, mild; others disabling) continues – maybe a ~5% chance in a vaxxed person. Some will look at those odds as being concerning enough that they'll continue to act very cautiously. I probably won’t, but it’s an understandable choice. (17/20)
And others who have lots of contact w/ very vulnerable people – unvaxxed who didn’t get Omicron, for example, or immunosuppressed – may also make different choices. That’s entirely reasonable. This is very personal stuff and these individual decisions should be respected. (18/20)
As for me, this is why the community prevalence (cases, test pos %) will dominate my decisions. If they don’t plummet, I’ll keep my guard up until they do. And while I’m reasonably confident about the Spring, my confidence level falls as we move to later in the year. (19/20)
I hope this helps as you think about your own risk calculations... particularly why it's perfectly rational to be acting very cautiously now, while planning (& hoping) to make some different – & equally rational – decisions re: masking, dining, travel, etc. in 1-2 months.(20/end)

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More from @Bob_Wachter

May 19
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
In the Pax clinical trial, rebound was seen in 2%, so clearly we’re seeing a big difference in real-life use. If the poll results are even close to accurate, we need urgent study by @pfizer & @US_FDA to answer questions about a medication being Rx'ed 20K times a day in U.S.(3/13)
Read 13 tweets
May 18
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)
…tested positive Sunday May 8. She felt awful (terrible headache, congestion, fatigue) on Sunday and Monday; she began Paxlovid Monday, May 9. By Tuesday, she was feeling much better (which she attributed to the Paxlovid, though who really knows). She stayed in … (3/25)
Read 25 tweets
May 9
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)
… get much better than it is now for the next several years. So last week (M-F), she taught at a writing workshop – there were about 45 attendees and 5 instructors. Course attendees had a vaccination requirement. Masks were optional. The attendees & instructors… (3/23)
Read 23 tweets
May 4
The steady drumbeat of cases, coupled w/ CDC’s finding that 60% of Americans have had Covid cdc.gov/mmwr/volumes/7…, 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)
Nevertheless, I don’t think it’s inevitable that we’ll all get Covid in 2022-23. For folks (like me) who have dodged the bullet so far, I’m fairly – but not 100% – confident that we can remain Covid-free by acting prudently, adjusting behavior based on the current threat.(3/25)
Read 25 tweets
May 2
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)
I'd still like to avoid Covid (mostly worried about Long Covid symptoms & long-term risks (heart/neuro/diabetes); also disruption of daily life). I'd slipped a bit re: masking in non-crowded spaces, & gotten less careful re: restaurants. I'm resuming more cautious behavior. (3/4)
Read 4 tweets
Apr 17
I’ve been gratified hearing from many people who have said that they’ve followed my lead in deciding what they'll do, and not do, in various stages of the pandemic.
It’s a particularly confusing time now, so today’s 🧵 is a summary of the choices I'm making these days. (1/25)
I’ll get to these choices later (if this is TL;DR, skip to 15/25). But to understand them, you need to appreciate my own risk, risk tolerance, & synthesis of the evidence – since as rules melt away, choices will be increasingly personal, often without clear “right” answers.(2/25)
Here goes:
1) I’m 64, pretty healthy (mild asthma, mild high cholesterol). So I have a moderately ⬆risk of a bad outcome from a Covid case (compared w/ a younger person), but not super-high.
2) I live in San Francisco, which remains a careful city when it comes to Covid… (3/25)
Read 25 tweets

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