I am starting to believe type O might be less susceptible. My momma is O and she rarely if ever gets noro, and if she does get a belly ache it is usually just that, a belly ache. i.e my daddy and brother both caught a stomach virus (don't know their blood types) and she hung around them and all she got was a bit queasy for an hour or so then nothing. I am type A and I have caught more than my fair share of stomach viruses.