As said in YS and OW, a Red Court Vampire (or Infected) can use its addictive saliva to perform Mental Stress Attacks – it's a Fight roll, usually against Athletics.
The vampire saliva is almost useless in combat situations though, since Might bonuses don't apply and their (high) Deceit skill can't be used for it. And though some vampires use their saliva to coat their weapons, I can't find any rules in DFRPG that would make this tactic effective.
In the books, however, a Red Court vampire's saliva is much more powerful, so much so that the main concern of Harry Dresden when fighting vampires is do not let them lick you.
I want Red Court vampire saliva to present this kind of danger in the game, but I'm not sure how to accomplish it with DFRPG's rules.
Best Answer
No, you're not missing anything, as far as the rule goes.
Red Court vampires use the narcotic saliva to manipulate people, not to injure them. That's according to the rule you cited, and that's according to all fictional positioning from the source novels.
The un-asked part of this question is about ways which a Red Court vampire could alter the flow and outcome of a physical fight, though. I'll answer it anyway.
Number one, there's no reason someone can't be Taken Out of a Conflict by taking too many hits on the Mental stress track as opposed to the Physical one.
Number two, these Attacks yield Consequences like any other physical or social Attack (if the relevant Stress track is full or inadequate). These Consequences represent the hold the vamp acquires over the victim, they come with free invokes (or, "tags", as they're referred to in DFRPG), and they can be Compelled.
Number three, Red Court vampires have plenty of other skills which they can employ to Maneuver once the influence of the saliva has begun to sink in. They're different kinds of Maneuvers - not the kind a brawler or a shooter would try to create, but the kind that a mental manipulator would try to create. End the fight by crippling the opponent's motivation or willpower.
You also mentioned Deceit and Might. If your Red Court vampire has high Deceit, she can use it to Maneuver for the sake of making the saliva attacks more sure to land, and to Maneuver for the sake of causing the fighter to miss their own attacks, so her low Might matters less. A character like this can take Stunts which allow her to use Athletics in place of Might, for a different way to achieve that kind of bonus.
In short, a Red Court vampire can win a fight against a heavier hitter with higher combat skills and a longer physical Stress track by making the fight their own, with tactics radically different from the bruiser's, and just enthrall or cripple them mentally till the punching stops.