Just going to base some ideas off what you said this perk could theoretically do.
Maybe instead of a zombie hitting you and becoming poisoned, maybe it is activated when you knife a zombie. It could be a way to power up your melee weapon after it has become near-useless on higher rounds.
Or your antivenom idea? Maybe the three-headed mutant zombie thing spews poison and you need to get it cured like in Advanced Warfare?
Maybe the image is the 'symbol' of sorts for the three-headed zombie too.
Just from like a minute of gameplay, I was impressed with this game. Now seeing 22ish minutes of gameplay, I'm much more than impressed. I hope this comes to consoles at some point since my computer is literally trash.