I have seen a lot of people obsessing with Table 5 of the 8/21 UK Delta report:

402 Covid deaths among 47,008 fully vaccinated for case fatality rate 0.86%

253 Covid deaths among 151,054 unvaccinated for CFR=0.17%

Do vaccines increase CFR 5-fold?
They also split data out by age (<50/>50).

For older group, CFR for vaccinated (1.81%) is 3.3-fold LOWER than CFR for unvaccinated (5.96%)

For younger group, CFR for vaccinated (0.05%) is 1.5-fold higher than CFR for unvaccinated (0.03%), but there are only 13 deaths.
Another case of Simpson's paradox, since a confounding factor (age) is STRONGLY associated with both outcome (death) and exposure (vaccination status) given risk of death in old >>> young and vaccination rate old >>> young.
Hopefully people soon realize that given the dramatic age disparities in vaccination and in risk of severe outcomes, any estimate of vaccine effectiveness must adjust for age by stratification or some other approach or it will give very confusing and misleading results.
Here is a brief blog post on this:
Just for fun, to show how EXTREME Simpson's effect can be, look what happens if we change the 13 deaths in vaccinated <50yr to 2 deaths.
In this case the CFR is HIGHER for unvaccinated for both <50yr (4.2x) and >50yr (3.3x), yet LOWER for unvaccinated if unstratified (5x).

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More from @jsm2334

15 Sep
Data presented below show nearly 33% of unvaccinated adult Israeli residents were previously infected.

Why is this important & has this contributed to misinterpretation of Israeli data?

This thread wll explore these questions.
Israeli MoH releases periodic vaccination reports on its Telegram site. This table breaks down vaccination status by age groups as of September 14, 2021 listing total population and number given 1/2/3 doses plus those unvaccinated but recovered from previous infection
2/n Image
From these data, I constructed this table with % of population unvaccinated, given 1 dose, 2 doses, & 3 doses, & proportion of unvaccinated are previously infected.

Note that >30% of total unvaccinated Israelis were previously infected, & >1/3 for all age groups in 20-59yr
3/n Image
Read 11 tweets
12 Sep
How well are vaccines and boosters really protecting against COVID-19 deaths?

Israel MoH publicly posted daily COVID-19 death data split by unvaccinated, boosted, and vaccinated-not-boosted from Aug10-Sept8

Here are results of my analysis of these data
Summing over all days, it is not promising to see so many COVID-19 deaths in vaccinated/boosted groups.
But by now we know better than to draw conclusions from raw counts, right?
The Israeli MoH dashboard provides enough information to infer total proportion of population unvaccinated, boosted, or vaccinated-by-not-boosted, so we can compute normalized COVID-19 death rates in these groups.

Read 13 tweets
24 Aug
New medRXiv paper by UPenn group led by John Wherry looking at immune markers 6m after vaccination.

Partially explains waning vaccine efficacy vs. infection, more durable vaccine efficacy vs. severe disease, and is relevant to current booster policy.

Paper measured immune markers (antibodies, T-cells, B-cells) from 61 individuals vaccinated with Pfizer/Moderna at 6 time points, from pre-vax to 6m post-vax.

16 were previously infected with SARS-CoV-2 and 45 SARS-CoV-2 naïve, and analysis was stratified by previous infection.
The key results were:
1.Neutralizing antibodies (NAbs) decreased over time
2.Memory B cells (Bcells) increased over time and did not wane
3.Helper T cells (T4) and Killer T cells (T8) dynamic described
Read 14 tweets
24 Aug
Great tweet by Monica Gandhi on new paper on transmission using the best way to track transmission: attack rate of virus after exposure in a rigorous contact tracing setting.

A few comments about what this might mean for transmissibility of breakthrough infections...
Although not dealing with breakthrough vs. unvaccinated infections, two results that are encouraging for the notion that breakthroughs might transmit less:
1. Asymptomatic infected were >4x less likely to transmit to others than symptomatic.

We know breakthrough cases are more likely to be asymptomatic, so this suggests one reason why breakthroughs might transmit less ...
Read 7 tweets
18 Aug
@CT_Bergstrom I agree Carl.
I will write a blog post on this but one possibility is that this is a combination of
1. unmeasured confounders (eg that young people vaccinated in January are Health care workers who are tested and exposed much more than those later vaccinated young people)
@CT_Bergstrom 2. Delta effect. Since we know delta spreads faster & with 50-100x viral load, it makes sense this higher viral exposure could lead to detectable virus that would produce “asymptomatic breakthrough infections” if testing done at right time, even if the vaccine works as intended
@CT_Bergstrom 3. And based on data I’ve seen showing memory B cells and helper T cells remain maxed out at 6m (and can produce new nAbs in 2-3 days)and nAbs and killer T cells decrease 10x but still remain 10-100x prevaccine baseline, it is possible that in early months the circulating nAbs..
Read 5 tweets
17 Aug
Many are confused by results that >1/2 of hospitalized in Israel are vaccinated, thinking this means vaccines don't work. I downloaded actual Israeli data datadashboard.health.gov.il/COVID-19/gener… and show why these data provide strong evidence vaccines strongly protect vs. serious disease (1/8)
Read 15 tweets

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