If you're an MD then I'm the Hamburglar.

The technical/scientific/medical definition of a vaccine has always been that it stimulates a person's immune system to recognize an antigen.

Nothing about whether or not it prevents a person from getting infected with something.

The notion of "the vaccine doesn't necessarily prevent you from getting infected so therefore it's not a real vaccine" is something that instinctively makes sense to the Facebook crowd, and has become a talking-point for idiots, but was never a real thing.