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David Dowdy

28 Sep, 21 tweets, 9 min read

Six months ago, 15% of Americans had been fully vax'd.

How is vaccine effectiveness (VE) holding up? I looked up VE estimates over time, state by state.

Long story short: VE has been remarkably stable over the last 2 months.

If immunity is waning, it's not waning fast.

California: VE 84% on July 31, 87% now.
bit.ly/39IiOy0

Colorado: VE 62% on Aug 1, 69% now.
covid19.colorado.gov/vaccine-breakt…

Connecticut: VE 81% on Aug 2, 79% now. portal.ct.gov/-/media/Corona…

DC: VE <70% on Aug 2, 71% now.
coronavirus.dc.gov/data/vaccinati…

Georgia: can't see the actual numbers, but bars for now vs July 26 look pretty similar.
dph.georgia.gov/document/docum…

Indiana: VE 68% on July 31, 79% now.
coronavirus.in.gov/vaccine/2680.h…

Louisiana: No data over time, but VE >85% now.
ldh.la.gov/coronavirus

Michigan: Exact numbers not visible, but VE is stable from July.
michigan.gov/coronavirus/0,…

Mississippi: If we believe these data, almost no breakthrough cases.
msdh.ms.gov/msdhsite/_stat…

Nevada: Southern NV Health District suggests VE is roughly stable, w breakthrough cases declining.
covid.southernnevadahealthdistrict.org/cases/

New York: VE 76% on July 26, 77% now.
covid19vaccine.health.ny.gov/covid-19-break…

Oregon: VE not available, but % of cases that are breakthrough was the same July 31 and Sept 11.

(The data from Sept 18 are the one instance of potentially falling VE that I could find - but are just 1 week of data.)

oregon.gov/oha/covid19/Do…

Rhode Island: only cumulative data available, but slopes look similar over last 2 months.
…through-cases-rihealth.hub.arcgis.com

Tennessee: Percentage of cases that are breakthrough went down between July and Aug.
tn.gov/content/dam/tn…

Utah: VE 72% on July 31, 84% now.
coronavirus-dashboard.utah.gov/risk.html

Virginia: VE 78% on July 31, 84% now.
vdh.virginia.gov/coronavirus/co…

Washington: King County VE 77% on July 26, 86% now.
kingcounty.gov/depts/health/c…

West Virginia: VE 72% on July 31, 85% now.
dhhr.wv.gov/covid-19/pages…

Wisconsin: VE 64% in July, 65% now.
dhs.wisconsin.gov/covid-19/vacci…

In the end, I couldn't find a single state with clearly falling vax protection from late July to now.

In some states, it was rising.

(And VE vs hospitalization was much higher than the estimates vs infection shown above.)

If immunity is waning in the US, it's not waning fast.

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David Dowdy

@davidwdowdy

26 Sep

@KCPubHealth

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.

Read 8 tweets

David Dowdy

@davidwdowdy

24 Sep

I applaud the ACIP for taking a nuanced stance.

But am hearing lots of concern from vax'd under-65s who are worried their immunity will be gone 6 months after their 2nd shot.

To address this, let's take a tour of 2 populations of about the same size: Israel and Virginia.

First, Israel. It's essential to debunk this myth:
"Israel vax'd its population first.
It now has high COVID rates.
Vax immunity must be waning."

This storyline has a lot of problems.

First, 50% vax coverage was only achieved 6 months ago (Mar 17), 4 mos before the surge.

So when the booster was made available in Israel on July 30, only 20% of its population had been fully vax'd for 6 months.

But at the time of the Israeli surge (July-Sept), most people had not been vax'd for >6 mos.

This surge was not caused by waning immunity.

Read 9 tweets

David Dowdy

@davidwdowdy

18 Sep

The big COVID news, dropped on a Fri afternoon:
"effectiveness vs COVID-19 hospitalization was higher for Moderna than Pfizer (and Janssen/J&J)."

bit.ly/3kjuoFR

But let's take a look at the analysis before accepting these results at face value...

1. Here are the data - on the surface, looks like Moderna effectiveness is constant at 92-93% after 120 days, Pfizer drops from 91% to 77%.

(btw, this was CDC not Pfizer funded, but what a great strategy for Pfizer - push "waning immunity" so people need a 3rd dose of your vax)

2. But note that the comparison group for all of these is the same - difference b/w numerator & denominator is always 1463 cases & 899 controls.

Meaning that people w Moderna & Pfizer (& J&J) are being compared to the same unvax'd folks.

Read 7 tweets

David Dowdy

@davidwdowdy

16 Sep

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.

Read 6 tweets

David Dowdy

@davidwdowdy

12 Sep

Dear FDA Advisory Ctte:

As you consider boosters for older Americans, ask yourselves *why*.

Is it to:
1. Slow transmission,
2. Boost long-term (waning?) immunity, or
3. Give short-term protection?

1. Will be a small effect
2. Has no data
3. May be the wrong time.

A thread...

1a. For transmission, look at the data from Israel. After giving booster shots, rates in those 60+ went down sharply.

But what was the effect on other groups? None.

ourworldindata.org/vaccination-is…

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.

Read 13 tweets

David Dowdy

@davidwdowdy

2 Sep

@NEJM

@NEJM joining the waning immunity debate. I'm going to push back a bit.

Data from @UCSDHealth of vax effectiveness in health workers: 94% in June, 65% in July. Interpreted as "likely to be due to...delta and waning immunity over time, compounded by end of masking requirements."

1. re: delta. ~50% of CA sequences were delta in June. So if delta were the driving factor, we would expect to see some waning of vax effect in June (~halfway between May & July) - which we don't.

2. Same thing with waning immunity. According to the paper, vaccination started in mid-Dec, and it took 3 months to get 76% of workers vax'd. Why then would we see no waning of effect in May or June - and then a sudden drop of 30% in July?

Same for mask mandate - lifted June 15.

Read 12 tweets

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