20% of blood donors infected (+ 63% vax'd) by May 2021: bit.ly/3mPkr37.
So pre-delta, likely at least 1/3 of unvax'd adults had been infected.
But 10m confirmed US cases (25% of total) have occurred since May - and most were in unvax'd adults.
Need to adjust for multiple infections, low testing in early 2020, etc.
But almost certain that >5% of US adults (=13m people) were infected in delta surge. Mostly unvax'd.
So, among US adults, estimate:
66% fully vax'd
>10% more (1/3 of remainder) infected by Dec 2020
5% more infected by May 2021
>5% more infected during delta
5% more (1/3 of remainder) w 1 dose
Again, caveat of multiple infections, but likely ~90% of adults have some immunity.
Waning immunity could lead to more cases.
But for serious illness, vax effectiveness remains very high, even rising - see below from CDC (bit.ly/3oVG30s).
Similar effect likely from natural immunity - not 100% protective vs infection, but very good vs severe illness.
New variants can always emerge.
But despite 4 months of intense transmission, no new variants have been able to compete with delta - in the US or worldwide.
Virtually every COVID case is still delta.
And as transmission declines globally, fewer mutation events are happening.
A new wave can start anywhere in the world.
(And the failure to share vaccines globally is a curse on our house as humanity.)
But other than in Eastern Europe, COVID deaths are largely falling worldwide. Even in places where our global vax response has been shameful.
Also encouraging: case rates are falling fastest in states (AL, FL, TN, MS) that had the worst delta surge.
While not rising much in states where vax levels are high.
This is what we would expect if immunity were playing an important role & vax effectiveness were holding.
Caveats: 1. Nobody can predict the pandemic future. 2. Kids are still at risk (though don't get as ill: bit.ly/3iYsMAs). 3. Trends reflect current behavior. If we relax too quickly, cases & deaths can rise again. 4. Outbreaks will occur among unvax'd. Keep vaccinating!
In summary:
- More US adults were likely infected w delta than are still non-immune.
- Likely <10% of adults have no immunity.
- Immunity against serious illness is holding.
- No variants have replaced delta.
Meaning: any future waves will likely not be as bad as the last one.
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A 🧵 for non-scientists on vax & boosters, using data from @KCPubHealth.
Seattle shows us "case relative risk", comparing unvax'd vs vax'd, over time (bit.ly/3ESvUqV).
Think of this as "level of vax protection".
Since late July, it's been stable, even going up.
Think of this number as "how many times more protected you are vs COVID if vax'd vs unvax'd."
There are 2 factors likely to affect this. 1. How long since your last shot (waning) 2. Level of exposure in the community (when exposure is intense, vax may not prevent all infections)
From mid-April to mid-May, "protection level" went up because:
1. People were getting their 2nd shots (upper right, dark bars = 2nd doses given). 2. Exposure levels were going down.
By May 16, vax'd folks were 20x more protected from getting COVID than unvax'd, on average.
A visual representation of what we know and don't know about waning immunity.
We know, at 6-8 months:
- Partial vax not great.
- Full vax ~70-85% effective (better vs severe disease than infection).
- Booster gives short-term bump.
We don't know what happens next.
4 scenarios:
Scenario A: Booster gives long-term benefit (by increasing immune memory), and immunity to 2-dose series continues to wane.
In this scenario, boosters are the right thing to do, now.
Scenario B: Booster doesn't improve immune memory, so the added effect of booster is short-lived.
This is the worst-case, and in my mind least likely - because vax has been effective, w/o booster, for 8 months now.
Here, booster helps a bit, but we need revised vax.
1b. This makes sense, because:
(a) in the US, people 65+ have the lowest case rates
(b) most of those cases are in not-fully-vax'd
(c) fully vax'd recover faster
(d) people 65+ have fewer contacts
Bottom line: to halt transmission, fully vax'd seniors would be lowest priority.