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American economist and author Paul Craig Roberts wrote in a blog article, CDC Admits that the Covid Pandemic Was the Product of an Inappropriate Test:

Quietly without media attention, the Centers for Disease Control and Prevention (CDC) has withdrawn the PCR process as a valid test for detecting and identifying SARS-CoV-2.

"After December 31, 2021, CDC will withdraw the request to the U.S. Food and Drug Administration (FDA) for Emergency Use Authorization (EUA) of the CDC 2019-Novel Coronavirus (2019-nCoV) Real-Time RT-PCR Diagnostic Panel, the assay first introduced in February 2020 for detection of SARS-CoV-2 only." [...]

The CDC admits that the PCR test cannot differentiate between SARS-CoV-2 and influenza viruses.

The linked CDC Laboratory Alert says:

In preparation for this change, CDC recommends clinical laboratories and testing sites that have been using the CDC 2019-nCoV RT-PCR assay select and begin their transition to another FDA-authorized COVID-19 test. CDC encourages laboratories to consider adoption of a multiplexed method that can facilitate detection and differentiation of SARS-CoV-2 and influenza viruses. Such assays can facilitate continued testing for both influenza and SARS-CoV-2 and can save both time and resources as we head into influenza season. Laboratories and testing sites should validate and verify their selected assay within their facility before beginning clinical testing.

I understand that the CDC is saying that because of the similarity between the symptoms of both diseases, "... a multiplexed method that can facilitate detection and differentiation of SARS-CoV-2 and influenza viruses" can "save both time and resources". I think that the claim that "The CDC admits that the PCR test cannot differentiate between SARS-CoV-2 and influenza viruses." is a deliberate misrepresentation.

Did the CDC say the test cannot differentiate between SARS-CoV-2 and influenza viruses? Can that be interpreted as meaning that the COVID pandemic is smaller than widely claimed?

Oddthinking
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Martín-Blas Pérez Pinilla
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    I think you need to narrow down what part of the claim you are questioning. Do you mean those two bullets to be questions? –  Jan 09 '22 at 17:25
  • @fredsbend, my question is "CDC Admits that the Covid Pandemic Was the Product of an Inappropriate Test?" The bullets are *my* initial impression. – Martín-Blas Pérez Pinilla Jan 09 '22 at 17:50
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    That's your title, and your words. From the quoted claim, the closest text is *"The CDC admits that the PCR test cannot differentiate between SARS-CoV-2 and influenza viruses."* So you're questioning "does that imply the pandemic didn't exist? Was actually influenza? Something else?" That doesn't appear to be part of the quoted claim. Answers *can* (and are encouraged to) address the implications of a factoid, but first need a direct claim to address as either true or not. –  Jan 09 '22 at 18:02
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    @fredsbend, I'm questioning the "**admits**". – Martín-Blas Pérez Pinilla Jan 09 '22 at 18:08
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    I agreed with @fredsbend that the title was confusing. I have edited it to focus on the claim you seem to be asking. (I avoid "admitted" because that is just an emotive term for "said". I avoided "product of an inappropriate test" because that doesn't seem to mean anything.) – Oddthinking Jan 09 '22 at 21:22
  • If the number of Covid infections is smaller than assumed, then since the number of deaths is unchanged, it means catching Covid is more dangerous than assumed. If tests give 90% false positives as some anti-vaxxers claim then catching Covid is ten times more dangerous than assumed. – gnasher729 Jan 13 '22 at 11:23

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The blog post you linked is entirely based on a fundamental misreading of the CDC statement. The CDC did not say that the original tests cannot distinguish between SARS-CoV-2 and influenza. And this statement is also categorically false; the original tests will not create a positive result in a patient with influenza.

The CDC has written the following in the notice that is linked from the blog post:

CDC encourages laboratories to consider adoption of a multiplexed method that can facilitate detection and differentiation of SARS-CoV-2 and influenza viruses. Such assays can facilitate continued testing for both influenza and SARS-CoV-2 and can save both time and resources as we head into influenza season.

The author of the blog post is interpreting this statement as "the SARS-CoV-2 PCR test would also test positive if you had influenza". They're a bit annoyingly vague in what they actually find that scandalous about the test, but I don't see any other interpretation that would be consistent with the blog post.

The CDC statement seems a bit ambiguous, but it is directed at an expert audience and not the general public. The only thing it actually claims is that the new tests can detect both and distinguish between influenza and SARS-CoV-2.

This does not mean that the old 2019-nCoV tests would mistake influenza for SARS-CoV-2, and you can verify that by looking at the FDA manual for these tests on page 45. There it lists the checks they did to verify that the test does not produce false positives when other viruses are present. They did specifically test for three influenza strains there.

As another point of evidence, I'll look at the first PCR test developed in Christan Drosten's lab, which was the template for many of the original tests (the US and CDC were a bit of an exception here). This test was published in "Detection of 2019 novel coronavirus (2019-nCoV) by real-time RT-PCR" and you can see in the paper that they tested 297 different samples from different viruses, and none of them caused a false positive. These samples contained six different influenza strains.

The advantage of a multiplexed PCR test is that you test for more than one virus. So in this case with the new tests this is the same as performing two tests at once, one for SARS-CoV-2 and one for influenza. With the old test you only get either "SARS-CoV-2" or "something else or maybe nothing". With the new test you get either "SARS-CoV-2" or "influenza" or "something else or maybe nothing". It is also useful to know if someone has influenza when deciding on treatment, and that is the reason the CDC recommends these new tests. The multiplexed tests provide more information, but that doesn't mean the old tests can't distinguish SARS-CoV-2 and influenza. They can detect the former, but they simply cannot distinguish the latter from other viruses or no virus at all.

user7761803
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Mad Scientist
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    'With the new test you get either "SARS-CoV-2" or "Influenza" or "something else or maybe nothing"' If you are nicely listing all the possibilities, didn't you likely forget the possibility that a patient could have both? – Nobody Jan 10 '22 at 21:46
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    @Nobody yes, that would also be a possible result. That is quite unlikely as far as I know, but these are essentially independent tests and both can be positive. – Mad Scientist Jan 10 '22 at 21:54
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    @MadScientist It's an event that [has been documented](https://www.timesofisrael.com/flurona-israel-records-its-first-case-of-patient-with-covid-and-flu-at-same-time/), with the catchy name of "Flurona." The catchyness of that name has increased the attention being directed towards the possibility that both may occur simultaneously. – Cort Ammon Jan 11 '22 at 01:02
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    @MadScientist: Quite unlikely because you'd have to be unlucky twice in a row, right? Nothing that Covid would protect you from flu and vice versa, except that social distancing etc. etc. protects you from flu as well. – gnasher729 Jan 11 '22 at 10:04
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    @gnasher729 not at all unlikely given that the majority of covid cases have no or very light symptoms and people just think they have a cold. So you think you have a cold, come down with the flu, and get a covid test as a condition of being allowed to see your doctor for flu treatment, which then finds both and the conspiracy theorists call it "flurona, a deadly new virus that's both flu and covid". – jwenting Jan 11 '22 at 15:03
  • "the original tests will not create a positive result in a patient with influenza" would be great to have a reference for this statement, as that is (I think) what the blog article seems to claim – user7761803 Jan 11 '22 at 17:25
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    @user7761803 that's exactly what the linked documents say. They detail the control experiments that were done to validate the tests, which included testing influenza samples and checking that the result was negative. – Mad Scientist Jan 11 '22 at 17:29
  • (@CortAmmon) Even earlier, one of the well-studied early cases involved [a child with detectable levels of covid, flu, and cold viruses](https://www.theguardian.com/world/2020/apr/21/boy-with-covid-19-did-not-transmit-disease-to-more-than-170-contacts) - but apparently didn't pass it on despite having symptoms (presumably the symptoms common to various respiratory viruses so maybe without the others he would have been an asymptomatic covid case) – Chris H Jan 11 '22 at 18:12
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    "the original tests will not create a positive result in a patient with influenza." ... and without Covid, I guess? – Paŭlo Ebermann Jan 12 '22 at 01:08
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    "Multiplexed" makes the meaning clear. In communications, it means transmitting multiple signals down a single channel. They want there to be one test that can detect and distinguish two things, not two tests than can detect only one thing each. – nigel222 Jan 12 '22 at 16:24
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    @nigel222 Multiplex PCR runs multiple targets in the same vessel on the same sample. It pulls off this trick by using different fluorescent dyes for each target. Each target uses a different optical channel. – Eric S Feb 03 '22 at 17:46