So, what happened was that in 2018 they changed the definition of vaccine from "innoculated bacterium/viral agent" to "any substance" (probably to make space for mRNA vaccines), and then changed the result from "that prevents disease" to "that generates antibodies".
Legally, a prophylactic seems to be the same as a vaccine, at least according to this definition from 2013: https://www.law.cornell.edu/definitions/uscode.php?width=840...