Searching that sentence verbatim on Google produces, as a first result, a paper on the National Library of Medicine [1] that states in its abstract:
> Extended mask-wearing by the general population could lead to relevant effects and consequences in many medical fields.
How is that a conspiracy theory? At most, you can argue that it's not absolutely conclusive or that other studies reach different conclusions. But that's far from declaring something a conspiracy theory.
I think some people consider information contrary to that communicated by government officials to be conspiracy theory: If the government didn't tell us the truth about something, they conspired to tell us something untrue.
By this definition of conspiracy theory, anybody who is not a conspiracy theorist is credulous. I proudly call myself a conspiracy theorist AKA skeptic.
> As a library, NLM provides access to scientific literature. Inclusion in an NLM database does not imply endorsement of, or agreement with, the contents by NLM or the National Institutes of Health.
That's a banner at the top of the page.
Science is not done by consensus or endorsement. Studies must be refuted on scientific grounds.
Studies that disagree with your opinion are not conspiracy theories.
Heaven forbid! It's almost comical how certain people furrow for the tiniest of cherries to support their antivaxx, antimask knee jerking while their bodies get submitted to a gauntlet of health risks from contracting COVID.
Your original argument was that this is a conspiracy theory, and it isn't.
Flu shots are indeed a vaccine.
I think you're confused by the word "immunity". In the medical sense, it doesn't mean "invincibility". It's a reference to the immune system!