Walenshy on rapid tests … then and now.

Last week, we spotlighted a NY Times article “The C.D.C. Is Hoping You’ll Figure Covid Out on Your Own”.

Author Zeynep Tufekci asked:

Why, two years into the pandemic, are people are grasping to know whether they should see a grandparent or an elderly relative or go back to work if they are still testing positive?

Why are we still trying to figure this out on our own?

Of course, the primary root causes are a new, fast-moving, ever-changing virus … and haphazard science, heavily politicized, that can’t seem to converge on a coherent “theory of the case”.

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Now that Biden’s test kit program is about to launch, this part of the article has specific relevance….

Deep in the article, Tufekci  channels CDC Director Walensky to provide a clear explanation of covid testing … and an example of the politicization.

According to Tufekci…

Back in 2020, when Walensky was on the faculty of the Harvard Medical School and chief of the division of infectious diseases at Massachusetts General Hospital, she co-authored a scientific paper titled “Saliva-Based Antigen Testing Is Better Than PCR Swabs”.

Some snippets from that paper:

> PCR tests can detect tiny amounts of the virus, so they do a great job of “diagnostic testing” — determining early-on if you are infected and may require isolation or treatment.

> But, PCR tests can “return positives for as many as 6-12 weeks … long after a person has ceased to need medical care or pose any real risk of transmission to others.”

> Said bluntly: PCR tests do a good job of diagnostic testing but a rotten job of “surveillance testing” that zooms in on whether a person is contagious to others.

> “The antigen tests are ideally suited for surveillance testing since they yield positive results precisely when the infected individual is maximally infectious.”

The reason is that antigen tests respond to the viral load in the sample without biologically amplifying the amount of the virus. PCR tests do amplify the virus in the samples and sometimes detect and report inconsequential “left over” viral fragments.

> A rapid test turns positive if a sample contains high levels of the virus, not nonviable bits or minute amounts — and it’s high viral loads that correlate to higher infectiousness.

With respect to viral transmission: “False negatives” on rapid tests are a benefit since “those are true negatives for disease transmission”

Again, a PCR test is positive if any amplified viral content is detected.

An antigen test may be negative if the virus is present but the viral load is very low … consistent with a low likelihood of viral transmission.

> But, antigen tests may be slower (than PCR tests) to detect the early onset of an infection, especially if symptoms haven’t materialized, since the viral load may be low but building.

> So, confirming a suspected early stage infection is best done with a PCR test or with a series of rapid tests, say, every other day for a week.

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OK, that’s what Walensky said back in fall of 2020, before her shift from “scientist” to “political scientist”.

Now, she’s saying:

“We actually don’t know how our rapid tests perform and how well they predict whether you’re transmissible during the end of disease”

Has the science changed … or, the scientist?

Hmm

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P.S. Walensky’s entire 2020 paper is worth reading.

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