Varroa doesn’t cause deformed bees or slimy comb; it just weakens the bees such that they can’t effectively maintain the health of the hive, especially over winter, causing the hive to die out. While Varroa can also be a vector for other pathogens, it’s the effect on hive population before the winter where it’s most harmful.

(I’m a beekeeper in the US, so Varroa is something I’m unfortunately too familiar with.)

That said, I’d much rather deal with Varroa than AFB any day as it stands today. The current required action for AFB in my area is burning the entire hive including the woodenware. A vaccine to prevent AFB would be fantastic, as it’d remove the one thing that I’m actually concerned about from getting into my apiary.