The sequences of the influenza virus and SARS-CoV-2 have nothing in common
An article is circulating on the internet claiming that PCR diagnostic tests that detect cases of covid-19 actually find flu positives, because the FDA "instead used regular flu viruses" to produce these tests. This is FALSE. The FDA has not published a document claiming such a thing. In fact, it was based on the genetic sequence of SARS-CoV-2 to develop it and there are documents that show this.
"Since Fauci flu in any of its 'variants' has not yet been properly isolated, the FDA instead used regular cold/flu viruses to produce PCR tests, meaning that all those who test 'positive' for Chinese germs actually only test positive for seasonal flu."
The PCR, which stand for Polymerase Chain Reaction, is a technique invented in 1985 allowing the number of DNA copies in a sample to be increased exponentially. The swab is inserted into the nose and the sample is taken to be tested for fragments of the genetic material of a particular pathogen. In the case of covid-19, the search is for a SARS-CoV-2 RNA molecule.
The rumour that the current PCR tests do not detect covid-19 but influenza comes from the US Food and Drug Administration (FDA) allegedly publishing an article in which it "openly admits that the infamous PCR test for Wuhan coronavirus (Covid-19) was developed not with actual Chinese virus samples, but with what appears to be genetic material from a common cold virus".
However, the article does not link to the document in question, nor has the FDA published such a thing. In fact, the documents indicating the performance of the CDC 2019-Novel Coronavirus (2019-nCoV) Real-Time RT-PCR Diagnostic Panel, the first test approved for emergency use in the US by the FDA published in January 2020, indicate that the test is based on genetic sequencing of SARS-CoV-2, obtained through the GISAID database.
Perfectly isolated virus
Elsewhere in the article, the author insists that "the 'Fauci flu' [as he refers to the coronavirus] in any of its 'variants', has not yet been properly isolated", which is also false. Firstly, the virus has been isolated since the beginning of the pandemic and numerous peer-review scientific studies have been published explaining this process. Isolating a virus basically means being able to reproduce it in large quantities in a laboratory to study it. An example of a study specifying the isolation of SARS-CoV-2 is this one from January 2020, which in addition to publicising the virus to the world, specifies how the virus was isolated from pneumonia patients in Wuhan for study in cell culture.
On the other hand, what scientists isolate is not a disease (the 'Fauci flu' that the message talks about), but the virus that causes it; and secondly, the term 'Fauci flu' is not usually used in rigorous information channels, but on pages that consider that SARS-CoV-2 was a laboratory invention. Here we explain why this theory has no scientific basis.
Tests detecting more than one disease
Finally, the sequences of the influenza virus and SARS-CoV-2 have nothing in common, so false positives for covid-19 in patients with influenza are impossible.
Another thing is to implement a test capable of detecting and differentiating the diseases, which is precisely what the US Centers for Disease Control and Prevention (CDC) has proposed. In July 2020, they issued a prospectus explaining how new types of PCR tests would work, incorporating the ability to detect, in addition to SARS-CoV-2, two types of influenza viruses (A and B), which would save doctors time in diagnosing the type of illness ahead of the start of the seasonal flu season.