I’d suggest you’re talking about “a definition” not “the definition”. Merriam-Webster is just a dictionary, not the final authority on the meaning of words.
“The definition” would refer to how people actually use the word, and examples of pre-2020 writing (as I gave) where e.g. the vaccine for Marek’s is called a vaccine would suggest merriam-webster’s definition was too limited.
That said, I think the old Merriam-Webster definition still applies to the covid vaccine anyway, so this is a bit of a side conversation. “ produce or artificially increase immunity to a particular disease” an increase of immunity suggests that this definition also covers leaky vaccines.
The definition update seems to be more about, as sibling poster said, the first part of the definition not covering mRNA or toxin based vaccines accurately.
“The definition” would refer to how people actually use the word, and examples of pre-2020 writing (as I gave) where e.g. the vaccine for Marek’s is called a vaccine would suggest merriam-webster’s definition was too limited.
That said, I think the old Merriam-Webster definition still applies to the covid vaccine anyway, so this is a bit of a side conversation. “ produce or artificially increase immunity to a particular disease” an increase of immunity suggests that this definition also covers leaky vaccines.
The definition update seems to be more about, as sibling poster said, the first part of the definition not covering mRNA or toxin based vaccines accurately.