Archive for September 24th, 2021

More covid math: What about booster shots?

September 24, 2021

In yesterday’s post, we squeezed some data from Israel’s Dept. of Health.

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Analyzing that data, we concluded:

> Vaccinated patients accounted for almost 65% of Israeli covid deaths in August

> But, the death rate among the unvaccinateds (181.7 covid deaths per million unvaccinated adults) was more than double that of the vaccinateds (81 covid deaths per million among vaccinated adults)

> So, the implied effectiveness of the vaccine (protecting against death from covid) was 55%

OK, let’s move the ball forward…

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The case for boosters

Let’s assume that our analysis of the Israeli data is correct and the implied death prevention effectiveness rate of the Pfizer vaccine has, in fact, waned down to 55%.

Question: What if the vaccinated Israelis had all gotten 3rd shots that boosted their protection back up to, say 90%?

From yesterday’s analysis, we concluded that the monthly death rate among unvaccinated Israelis (in August) was 181.7.

So, at a 90% effectiveness rate — if all were boosted — we would only expect 18 deaths per million vaccinated people (1 – 90% = 10% of the unvaccinated rate).

At that rate, about 300 of the 389 vaccinated deaths would have been saved (18 deaths per million x 4.8 million boosted vaccinateds= 86.4; 389 – 86.4 = 302.6).

That’s about a 75% reduction in vaccinateds deaths… and about a halving of the total death count (218 + 389 = 607; 302.6 / 607 = 49.8)

Those are pretty compelling numbers in favor of booster shots…

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But, Pfizer’s numbers differ

Here’s an interesting twist to the story…

In Pfizer’s booster application, the company presented data indicating that the efficacy of its vaccine only waned slightly

Specifically, Pfizer claimed  that it’s vaccine’s effectiveness  against hospitalization (and, presumably, death) declines from 96.2% percent at seven days after dose 2 to 90.1% two months later to 83.7% six months later.

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Source

Stating the obvious: 83.7% is a high level of effectiveness … and much higher than 55%.

Think about that for a minute, though…

Based on Pfizer’s data, the vaccine is highly effective preventing hospitalization and that effectiveness does not wane very much over 6 months.

So, presuming that the grand objective is prevention of hospitalization and deaths, Pfizer’s data seems to weaken its  case for booster shots.

Sure, it’s always better to have more immunization than less … but, is a boost from 84% to 90% statistically or operationally significant? Is it worth the cost and incumbent risks?

Hmm.

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CAUTION

Don’t draw any hard conclusions yet!

There’s much more to the story that we’ll get into next week.

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DISCLAIMER: I’m not a medical professional or scientist — just a curious, self-interested guy.  So, don’t take anything that I say or write as medical advice. Get that from your doctor!
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Thanks to DF for pointing me to the Pfizer data

 


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