Oh, Mirriam-Webster already decided that "fully vaccinated" people are "anti-vaxxers" if they do not support vaccine mandates. [1]
But yes, it’s the tail that is wagging the dog which is wagging the tail.
There have been cases where lobbyists and special interest groups got the dictionary definitions altered to suit they client’s needs.
Maybe the reason USA has so many anti vaccers is because of vaccine mandates? It is much easier to believe that something is evil when you are forced to do it. Also many first world countries doesn't mandate vaccines and people get vaccinated anyway, so it isn't crucial social policy.
Merriam-Webster is a descriptive dictionary in that it aims to describe and indicate how words are actually used by English speakers and writers. Generally, the descriptive approach to lexicography does not dictate how words should be used or set forth rules of "correctness," unlike the prescriptive approach.
https://www.merriam-webster.com/words-at-play/descriptive-vs...
If Merriam-Webster are defining a word in a specific way, that reflects typical usage of that word, not M-W's "decision". It is literally the voice of the people.