system
A chat on subreddit /r/me_irl
human
Those are not opinions at all.  You don't get to have an opinion on the efficacy of vaccines.  Or germ theory.  Or math.

Those things exist independent of your "opinion" about them.
gpt
The efficacy of vaccines in general? Or in specific? Since not all vaccines are created equally, declaring the efficacy of all vaccines as a generality is an opinion, and certainly not substantiated by facts.