A:The Eradication Bonus can be “triggered” over and over again on any turn. The Zombie Boss and Adrenaline Bonus are both what we would call “formulaic bonuses”: they add to the number allocated for your official Draw and/or Play, which have a limit of “on your turn” (or “each turn” which is meant to be “each time your turn comes around”). Eradication Bonus, by contrast, is in addition to whatever you might Draw for your official Draw allowance, so it is not limited by the one-time nature of one’s Draw allocation for the turn.
We hope that makes sense. Let me see if I can find the FAQs which discuss formulaic vs. additional bonuses…
So, here is an answer which describes formulaic bonuses like the Zombie Boss or Adrenaline Bonus:
For example, if the rules are currently Draw 2, Zombie Boss, then whoever meets the conditions that make them the Zombie Boss, is at Draw 2 (+1). How many you get to Draw on your turn is one number that counts for your whole turn once. That number may change during your turn, resulting in additional Draws (but not “un-draws”.) You may go from Draw 2 (+1) to Draw 3 (+1) and get an extra for your single total Draw allowance for the turn.
On the other hand, if you were to use Jackpot, and draw 3 extra cards, those don’t count towards your Draw allowance for the turn. You could be at Draw 2, play Jackpot, draw 3 more cards, then increase the Draw to Draw 4, and you’d still get to draw 2 extra, since Jackpot is on top of your official on-your-turn Draw Allowance, which went from 2 to 4.
Although it is a Rule, and not an Action, the Eradication Bonus does not mention “on your turn” so we’d consider this to be an extra card you get IN ADDITION to your Draw allowance, and therefore it is not limited to your once-on-your-turn Draw allowance. Whenever the number of Zombies changes from some to none, you get to trigger that extra card draw, which is separate from your Draw allowance for the turn.