Thread by @Bob_Wachter

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. erictopol.substack.com/p/the-ba5-story

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)

… that BA.5 is just another one. But, as Topol describes, BA.5 is a different beast, with a new superpower: enough alteration in the spike protein that immunity from either prior vax or prior Omicron infection (incl. recent infection) doesn’t offer much protection. Drat. (3/25)

As we did w/ original Omicron, we need to determine 3 things w/ each variant: infectivity, immune escape, & severity. We know BA.5 is worse on #1 and #2.
Severity is still unclear, but we're seeing worrisome upticks in U.S. hospitalizations (though not yet deaths). (Fig). 4/25)

As BA.5 becomes the dominant U.S. variant (Fig), its behavior will determine our fate for the next few months, until it either burns itself out by infecting so many people or is replaced by a variant that’s even better at infecting people. Neither is a joyful scenario. (5/25)

BA.5’s ascendency comes against background of a high case # plateau & fair # of hospitalizations. Current US case rate is ~ 1/7 of January’s peak (115K cases/d vs ~800K/d). But since we’re missing ~80% of cases due to home tests, today’s true case-rate isn't far from Jan’s.(6/25)

What else has changed? Mandates are gone – likely forever in most of the U.S. And most people have ditched their masks & are unlikely to put them back on, no matter how large the surge.
So it’s up to each of us to determine our own risk tolerance, and then own behavior. (7/25)

Before I get return to the implications of the BA.5 wave, let’s review the local data .
In SF, we’re averaging 427 cases/day (51/100K/d; Fig).
(Due to home testing multiply this by ~5 to get an apples-to-apples comparison w/ earlier eras.)
SF hospitalizations are 114, up…(8/25)

… 6-fold since April, well above the U.S. trend (Fig L).
@UCSFHospitals, our hospital numbers have been plateaued for 2 months. We currently have 42 patients in the hospital, still only ~1/3 of our January peak. And only 4 are in the ICU, a very low ICU:hosp ratio (Fig R).(9/25)

@UCSF, the fraction of pts admitted “for” (vs “with”) Covid is now 50%. In Jan, it was 2/3 "for", 1/3 "with".
washingtonpost.com/outlook/2022/0…
This drop in “for Covid” admits, & particularly the fall in ICU #'s, are the silver-est linings of current phase. Let’s hope they stick.(10/25)

Our asymptomatic test + rate, which has been 5-6% for a couple of months, has inched up – today it's 6.5% (Fig). Again, this is my go-to number to get a feel for the risk of maskless indoor gatherings. If 1 in 16 people who feel fine actually has Covid, spend enough time…(11/25)

… maskless indoors & it’s near-certain that you’ll get it. (If 6.5% of an asymptomatic population has Covid, in a crowd of 50 people, there’s a 96.% probability that someone there is pos.) This is particularly true since vax (even w/ 2 boosters) and/or prior infection… (12/25)

… now offer relatively little protection against infection, although they still remain enormously protective against severe infection & death.
In fact, this is one of the biggest implications of BA.5: a prior infection – including an Omicron infection as recent… (13/25)

…as last month – no longer provides robust protection from reinfection. And that old saw about hybrid immunity (vax plus infection) providing “immunity superpower” (& thus no need to be careful) is no longer true – we’re seeing such folks get reinfected within 1-2 months.(14/25)

Analogously, booster #1 offers relatively little protection vs infection. In fact, your 2nd booster (I got mine 10 weeks ago) is also not protecting you much against infection – its protective effect vs. infection seems to wane in about 2 months. nejm.org/doi/full/10.10… (15/25)

Does this mean you shouldn’t get boost #2? Absolutely not! In fact, I’ve been on the fence about boost 2 for folks not at very high risk (ie, below age 70). But recent data shows a powerful ⬆in protection from boost #2 (4-fold mortality reduction in people >age 50; Fig). (16/25)

Many ask: “Shouldn’t I wait on boost #2 until fall, when a new bivalent (combo of original & Omicron-specific boost) is available? For those over 50, I’d say no – there's too much Covid around and evidence of benefit from boost #2 is persuasive.
Pfizer/Moderna are now…(17/25)

…developing a booster targeting BA.4/5 (the one they’ve built vs the original Omicron will have limited utility against BA.5). If the new booster is highly effective (not guaranteed), I doubt that getting a 2nd boost now will block you from getting bivalent boost in fall.(18/25)

Given all of this, what should individuals do today?
As always, it depends on how you feel about getting Covid. As I discussed last week @washingtonpost (below), I’m still trying to avoid getting Covid, largely because of risks of Long Covid. washingtonpost.com/outlook/2022/0… (19/25)

So I still avoid indoor dining & will continue to wear an N95 in crowded indoor spaces until cases come way down.
(If you’re in the “I already had Covid so I’m not worried” camp, realize there’s no evidence that Long Covid risk from a 2nd or 3rd case is <that of case #1.)(20/25)

We need to change our thinking about the value of vax/boosting. Vax/boost remains hugely valuable in preventing a severe case that might lead to hospital/death.
But its value in preventing a case of Covid, or preventing transmission, is now far less than it once was. (21/25)

This means that to gather indoors safely, a vax/booster requirement – while better than nothing – isn't very reassuring. To do indoor gatherings safely, it’s really about good masking (& no indoor eating) and ventilation; adding pre-event rapid testing offers additional…(22/25)

… protection.
At a policy level, I can’t see mask mandates returning just because BA.5 case rates go way up. But if hospitals still filling up, particularly if we also have staff shortages, I think we’ll see mandates return in Blue states. It would be the right call. (23/25)

It seems clear that BA.5 will lead to an ongoing plateau, if not a moderate surge, lasting through summer & into fall. Beyond that, much depends on whether a new variant emerges to supplant it. Given the pattern of the past year, it would be foolish to bet against that.(24/25)

I wish I had a happier analysis of our current Covid state. But BA.5 is yet another Covid curveball to be dealt with, and it's not great news.
(And I wish that BA.5 was the only bad news in the U.S. these days.)
Despite all of it, I hope you have a happy & healthy 4th! (25/end)