The first time your immune system sees weird blood, it's like, 'what the fuck??' The second time, it's already been seen, so your immune system says, 'absolutely the fuck not'.
Madness string 112066
The more you think about it, the more you realise all vampire rules are just anti-Italian rules. Can't eat garlic? IN ITALY? Can't go out in sunlight? IN ITALY? Can't go near crucifixes? IN ITALY? Can't cross running water? IN ITALY?