I responded to a question received through email. Considering my response would be helpful to this site’s visitors, I am also sharing it here.
Concerning your question, “I wasn’t able to find material there to help me with the questions related to the subject of what happened to the flu.”
It is difficult, if not impossible, to give a definite answer to the question because of the lack of data and reference standards (flu virus) and then the funny “science” at the authorities, like the CDC and FDA. However, below I provide you with the most likely scenario for the disappearance of the flu (e.g., see here link, link).
Everything associated with a virus is based on PCR testing. However, by definition, these tests are scientifically invalid or false. This is because the tests never detect any virus, but a small fragment supposedly from the virus RNA. However, these fragments could be from many other sources, such as healthy body cell degradation, bacteria, the food we consume, the test itself (e.g., choice of test threshold cycles), etc. Therefore, such tests can mostly give false positives/negatives.
Another reason, not commonly understood or described, for the test results’ fakeness is the primer choice. The outcome of test results depends on the choice of a primer. In a simple analogy, one may consider a primer as a “bait” to selectively seek a pre-defined target (the RNA fragment).
Therefore, if one likes to see or ignore a particular “virus,” one can add or remove a particular primer. For example, after the COVID-19 vaccination, when it did not work, presumably, they changed the primer to detect a different “version” of the virus. They called it variants like delta, omicron, etc., described with the mutation narrative. It is just one of the tricks they play with.
Concerning the flu, it is quite possible that either they changed the primer or, more likely, got busy with COVID-19 primer or testing. More likely, the chosen primer overlapped with the flu one and was not recorded as flu. This made the flu disappear. However, the flu may reappear shortly when the primer is switched (labeled) back with the old or new primer.
Virus testing is a selective exercise depending on a particular primer used. That is why, as some said, jokingly how intelligent the viruses or variants are; they come only one at a time. It is just because desire (policy) of the authorities as to what they like us (the public) to see and when, and then throw a specific primer (for an imaginary virus or variant) into it, and voila, that “virus” or RNA starts appearing in the population (e.g., see here link, link). Welcome to modern illness “identifications” and their treatment development!
In short, no virus is/was out there, even for the flu. However, authorities and experts most likely selectively ignore primer and/or count it with the COVID-19 primer.
I hope this will help.