The CDC document that was discussed in @washingtonpost today… is now on line:…
The WashPo shared it with me before publication for reactions, and I'm quoted. Some thoughts follow. (1/13)
My overall view: we knew much of what's in here, but there's some new information & analysis. In some cases it's brand new, in others it clarified something we knew before. In virtually all cases, the new stuff's a bit worse than I expected. Here are the key findings: (2/13)
1) Delta is much more infectious than the original: they estimate an Ro of 5-9, vs. the 2-3 for the original, which makes Delta "as transmissible as chicken pox." We've been estimating Ro of ~6 for Delta, or ~2x as infectious as original. It may be a bit worse than that.(3/13)
2) They believe the period of infectivity is longer (high levels of viral shedding for 18, rather than 13 days). This will raise questions about lengths of quarantine and isolation, as well as appropriate timing of testing.(4/13)
3) As we learned in the CDC announcement 2 days ago, they're finding equal viral loads in noses/mouths of people with breakthrough infections as in infected unvaxxed people. Likely means that breakthrough cases can spread the virus more readily than we previously thought.(5/13)
4) Vaccine efficacy: several estimates; they tend to show ~80% efficacy vs. Delta (vs. the prior 95%). Thankfully vax IS still ~95% effective vs. serious infections. That the efficacy of the vaccines is holding up for serious infections is the main piece of good news here.(6/13)
5) Lower efficacy in selected populations: significantly lower efficacy (~70%) in nursing home elderly (Fig L) and in immunocompromised (Fig R) patients. These are likely to be the first groups made eligible for boosters. Hopefully soon.(7/13)
6) Waning of immunity: no new data here (that I saw) supporting Pfizer findings that mRNA efficacy wanes over time. But final bullet says protection from prior infection wanes after 6 months – adding to risk to those whose immunity was from prior Covid. They still need vax.(8/13)
7) Seriousness of Delta infections. Early UK/India studies pointed to more serious infections, then consensus seems to be that they were not more serious. This document supports the "more serious" stance. That's concerning.(9/13)
8) Notwithstanding all the noise about breakthrough infections, the case for vaccination remains enormously strong: they show an 8-fold reduction in cases, and a 25-fold reduction in hospitalizations and deaths with vaccination.(10/13)
9) That said, as more people are vaccinated, there'll be more people in hospital and more dying w/ breakthru infections (even though vaccines work! – it's just math). Estimate here: 9% of hospitalized pts & 15% of deaths in vaxxed pts. Seems a little high, need to confirm.(11/13)
My overall take: As the document says, "the war has changed." Data argues that universal masking is critical to block spread of Delta – a more infectious, and possibly more serious virus – particularly if it's true that vaccinated folks can be part of the chain of spread.(12/13)
Document also makes clear that we need a new & far more aggressive vaccination strategy (w/ everyone masking indoors until we're there) if we're to get ourselves out of this new & unsettling stage. The foe has gotten better at its job, and so the war has indeed changed.(13/end)

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More from @Bob_Wachter

26 Jul
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)
Read 20 tweets
15 Jul
If you're wondering how bad Delta really is, even in highly vaccinated SF (76% of >age 12 fully vaxxed) & still w/ a lot of masking (most folks in stores), we're seeing a pretty steep Covid uptick. Daily cases up 4-fold (10->42; Fig L), hospital pts doubled (9->19; R)(Thread 1/4) ImageImage
Uptick mirrored @UCSFHospitals: Covid inpatients (we were at ~3 pts two-wks ago) now 13 (Fig L). Overall test positivity rate was well below 1%; it's now up to 2.6% (Fig R). Even more worrisome, test positivity rate in asymptomatic pts was ~0.15%, now up 6-fold to 0.9%. (2/4) ImageImage
I don't have vaccinated/unvaxxed breakdown for SF & UCSF – I assume most severe cases are in unvaxxed. But even for vaxxed, w/ more Covid in air expect more breakthru cases. As for me, I'm back to double-mask in stores. Still indoor dining but might abort if trends continue.(3/4)
Read 4 tweets
13 Jun
Covid (@UCSF) Chronicles, Day 453

1/ I know everybody’s sick of playing 3-dimensional Covid chess. Sorry, but the Delta variant forces us back to the chess board. Ergo, this 🧵.
If you’re fully vaxxed, I wouldn’t be too worried, especially if you’re in a highly vaxxed region.
2/ If you’re not vaccinated: I’d be afraid. Maybe even very afraid.
Why? Let’s start with the things that we know about the current situation, then layer in new information about the Delta (aka, Indian) variant, B.1.617.2 Then we’ll end with what I’d suggest you, and we, do.
3/ Current U.S. situation is good. Cases, hospitalizations, & deaths are falling fast, largely due to our fabulous vaccines. In SF – w/ 70% of people aged >12 fully vaxxed – we’re nearly in a post-Covid world. Everybody’s opening up, including (on Tues) CA. That’s fine…for now.
Read 25 tweets
18 May
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.
Read 25 tweets
18 Apr
Yesterday’s @WashingtonPost piece on flying-after-vaccination, in which I said I won’t eat on an airplane, created a bit of a kerfuffle.… Even @natesilver538 weighed in today.

Let me explain my thinking. (A 🧵) (1/25)
I am fully vaccinated (2 doses of Pfizer in Dec/Jan). As such, I consider myself exceedingly unlikely to get very sick and die from Covid, though as the number of vaccinated people grows, we are beginning to hear about a few breakthrough infections.… (2/25)
Most breakthrough infections are mild but there are rare ones that are serious. Of >75M people fully vaxxed as of 4/13, CDC has logged 5814 breakthrough infctns (documented Covid post-full vaccination). That’s not surprising. As we know, the vaccines aren't 100% protective.(3/25)
Read 25 tweets
4 Apr
1/ Covid (@UCSF) Chronicles, Day 383

Perhaps the most confusing time since the start of the pandemic – its easy to be overwhelmed. I’ll try to make sense of some of the key trends, particularly the “4th surge” & vaccines vs variants.

Bottom line: I’m still leaning optimistic.
2/ Part of my optimism stems from where I live: Covid stats in San Francisco are excellent. Let’s start w/ @UCSFHospitals, where there are 7 Covid pts (vs. ~100 in January), & only one on a vent (Fig L). Test positivity is 0.9%; 0.4% in asymptomatic patients (R). Pretty darn low. ImageImage
3/ SF overall is also good: 37 cases/day in city of 875K, maybe a tiny uptick in past few days (Fig L). Only 21 Covid pts in all SF hospitals (vs. 259 in January; R). And only 6 Covid deaths in SF in past 4 weeks; total deaths remain <500 for pandemic. Test positivity also 0.9%. ImageImage
Read 25 tweets

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