Archive for October 8th, 2021

Covid data: More about breakthrough infections and viral transmission…

October 8, 2021

As we posted yesterday ……

In its recent application to get an Emergency Use Authorization for booster shots, Pfizer submitted data indicating that effectiveness against infection starts high (90% immediately after the 2nd shot) …  but it wanes down to around 40% 6 months later.

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Source

From this data, we can infer some things about viral transmission … since infection is an obvious prerequisite to transmission.

Early on, soon after people get vaccinated, the risk of infection is very low, so the risk of transmission is very low.

But, as the vaccine’s protection from infection wanes, the transmission risk (among vaccinated people) increases.

The impact is, shall we say, statistically significant.

How significant?

Let’s run some numbers…

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How many transmitters?

In rough numbers that are good enough to calibrate the transmission impact, about 200 million people have been vaccinated and about 100 million haven’t been.

Using those ballpark numbers to determine the magnitude of effect …

In the spring, shortly after the first rush-to-get-vaccinated, there were about 100 million unvaccinated people who were vulnerable to infection and, thus, transmission.

At the same tome, 10% (the inverse of 90%) of the vaccinated people, about 20 million, were vulnerable to infection and transmission.

So, the total number of people vulnerable to infection and transmission was 120 million.

But, 6 months later, as the vaccinations aged & waned, 60% of the vaccinated people, about 120 million were vulnerable to infection and transmission.

So, the total number of people vulnerable to infection and transmission was 220 million … over half of whom were fully vaccinated.

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So what?

Everybody knows that cases started spiking this summer.

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The culprits behind the spike: the Delta variant … and unvaccinated people.

Or, so we’ve been told,

Delta is guilty as charged, but …

Because of the aging of Spring vaccination shots … and the associated waning of infection protection … our rough-cut estimate is that, pre-booster shots, more than half of the people spreading the virus are probably vaccinated people whose infection protection has waned.

They’re unindicted (and unnamed) co-conspirators behind the spike in cases.

In stats-speak: Bayes is alive and well … but oft-overlooked.


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