This zombie gains additional health when he hit someone.
Example: if Vampire zombie hit someone with 35 damage, that means he will
get 35 x 2 = 70 hp (35 is damage, 2 is damage multiplier)
If you're Nemesis you'll get 250 x 2 = 500 hp (250 is damage, 2 is multi)
On Single/Multi infection rounds zombies cannot damage humans, only infect, so Vampire Zombie will gain additional 1500 hp when he will infect someone