Well consider this - White Leghorn chicks reared in a sterile environment never develop ABO blood groups. This suggests that some at least of our blood groups (e.g. "I am A+") are the result of an infection.
The only people who seem to be at risk of serious illness or death from swine flu are those with underlying health issues.Most who have had it have reported it as being like a mild form of normal flu.
I have emphysema and i'm still unconcerned about swine flu.If I get it then I will deal with it,until then I won't worry.