Well, I don't believe that the COVID vaccine works, per se, but I'll leave the example out of this. I don't normally like arguing against other Christians. Except the one who thinks Trump leads a death cult. That one's fun.
Anyways, then it becomes satire. If you say "hey, it's just a meme", it either means that that's not the way they meant it (As in, it's being taken too literally- it wasn't meant to be read between the lines), or they forfeit the supposed truthfulness of the statement. In the latter, the meme that you made arguing against vaccination becomes satirical. Using memes to send important messages is unusual- memes are expected to be humorous, meaning that memes are a bit of a fickle medium. Sometimes you're taken too seriously, and sometimes those who understand they can be used for serious purposes will miss the joke in a comedic meme.