Caution is advised on blanket statements because there are several wholy different technologies in widespread use. Adjuvants are often not used for vaccines which work by giving you either a related ailment (e.g., cowpox/smallpox) or a genetically modified variant of some virus which may contain some elements of the 'real thing' and is supposed to make a person somewhat sick fighting off the 'fake one' leaving immunity covering the 'real one' as well.
Inert placebos are almost never used with vaccine safety studies. Doing so would result in the safety test failing because vaxxed group would drop like flies while the placebo group would be fine. The always use as a 'placebo' a DIFFERENT vaccine. In some of the covid vax tests they are using meningecoccal as much as they can, but Del Bigtree claims that his and Kennedy's 'ICAN', through a lawsuit, got some of the Moderna testing to be performed against inert placebo (saline.)
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I generally like the idea of letting one's own healthy immune system which, as you point out, has gotten us through millions of years. But...it is the case that current bioengineering technology can devise goodies which can defeat nature's work. If we allow 'leaders' who would consider the pleb classes of 'useless eaters' their enemy to do so, they will absolutely use this technology for their own ends.